Multimodal Corridor Planning
- Details
- Last Updated on Thursday, 12 June 2014
Article
Level of Service (LOS) is a classification system which uses the letters A, B, C, D, E, and F to describe the quality of the mobility our transportation system provides for automobile traffic, pedestrians, bicyclists, and transit. LOS A represents the highest level of mobility, while LOS F represents the worst. The Florida DOT Quality/Level of Service Handbook uses the graphic shown in this PDF to visually depict LOS A - F for various modes of travel. LOS is closely related to the concept of capacity, which measures the quantity of traffic moving across a given point.
Measuring LOS is a complex process, particularly for multi-modal facilities due to the interaction between modes. This guide does not intend to provide instructions on how to complete the wide array of detailed calculations required to determine LOS. There are several "state-of-the-practice" resources that go into those details:
- For pedestrian LOS, Florida DOT's Pedestrian LOS Model and the City of Charlotte's methodology for pedestrian LOS (TRB's Highway Capacity Manual also has a module for pedestrian LOS)
- For transit LOS, TRB's Transit Capacity and Quality of Service Manual (TCQSM) (see related documents in thePDFs tab above)
- For bicycle LOS, the Bicycle LOS Model, the Bicycle Compatibility Index, and the City of Charlotte's methodology for bicycle LOS (see related PDFs) (the Highway Capacity Manual also has a module for bicycle LOS)
- For vehicular LOS, TRB's Highway Capacity Manual, 2000 edition. TheCity of Charlotte also provides guidance on inclusion of multimodal factorsthat influencevehicular LOS.
Pedestrians
Pedestrian LOS is determined by the following factors:
- Existence of a sidewalk along the arterial
- Amount of lateral/horizontal separation betweenpedestrians and motorized traffic
- Volume of motorized traffic on the arterial
- Speed of motorized traffic on the arterial
In areas with a significant pedestrian presence, actual pedestrian counts should also be considered.
TRB's Highway Capacity Manual provides a precedent for this approach. A variety of data is gathered for these four variables and used in a set of mathematical equations to obtain a score, which is then translated to a corresponding LOS.
Transit
LOS for Transit is primarily determined by frequency of service, as shown in the figure at right. As future MetroLink expansion considers on-street services, street car/trolley LOS will also be an important consideration. Quality and level of service for these modes also considers the type of shelters and stations provided at stops along the various routes.
Bicycles
Five key variables, listed below in order of importance,are used to determine bicycle LOS:
- Average effective width of the outside vehicular through-lane of travel (includes striping for bike lanes)
- Volume of motorized traffic on the arterial
- Speed of motorized traffic on the arterial
- Amount of heavy vehicles/trucks on the arterial
- Condition of pavement over which bicyclists are expected to ride
Like the Pedestrian LOS Model, a variety of data is gathered for these five variables and used in a set of mathematical equations to obtain a score, which is then translated to a corresponding LOS. It is important to note that the Bicycle LOS Model applies to on-street
facilities, and not pathways or sidewalks.
The Bicycle Compatibility Index (BCI) is another model that was developed to predict the overall comfort experienced by a bicyclist on a given facility. The comfort level ranges from 1 to 6, with 1 being the most compatible rating and 6 being the least/worst. The index is based on qualitative comfort measures. See the BCI summary PDF and related links for more information.
Vehicles
For arterial streets and vehicular LOS specifically, areas are of interest are divided into two categories:
- Intersections: Quality and level of service at intersections control the overall quality and level of service for the broader arterial street. The intersections, particularly those signalized, are the points of greatest conflict and greatest safety risk for all modes of travel. Intersection quality and level of service is expressed in the amount of delay experienced at the intersection. It is important to recognize that most traditional evaluation methods are auto-oriented and do not account for the relationship between automobiles and other modes of travel. The City of Charlotte recently developed guidance for measuring signalized intersection level of service in multi-modal settings. The guidance is intended to yield a level of service for vehicular traffic in a way that accounts for pedestrian, bicycle, and transit impacts at the intersection. See the Charlotte Urban Street Design Guide: Vehicular LOS for Multimodal Intersections for more information.
- Street segments: The street segments are the sections of the arterial street between the intersections. The quality and level of service for street segments is traditionally expressed by the average speed by which vehicles can travel along the particular segment of the arterial street, although as noted above, the efficiency (or lack thereof) of the intersections will control the capacityand LOS of the arterial as a whole. As with intersections, street segment evaluation methods are traditionally focused on vehicular LOS. The City of Charlotte provides good guidance that account for multi-modal needs along the street. See the Charlotte Urban Street Design Guide: Segments for more information.
Planners and designers often refer to the "design year" when considering improvements for a vehicular street. The design year represents the planning horizon for the facility. For example, reconstruction of Manchester Road today would require the examination of some point in the future to determine the types of factors that must be considered in planning and designing improvements that will serve the future needs of the facility. Planners and designers will often examine the anticipated LOS for the design year of a facility in an effort to make sound decisions about current improvement recommendations.
Future traffic estimates, land use and development projections, population growth, and a variety of other factors all go into the determination of how much travel demand a facility is expected to serve at some point in the future. These projections are estimates based on assumptions ofhowdevelopment willaffect futuretraffic. They are meant only to give an approximation of what the future condition might look like.They should be one of many factors to consider when planning and designing great streets.
It is not uncommon for planners and designers to establish a target for future LOS performance. The Missouri Practical Design Guidesuggests that LOS E be the target for vehicular capacity in the design year for the urban/suburban place types considered in this guide. This is a target, it is not a mandate. The nature of the streets that we are concerned with will inevitably present situations where it is not possible to obtain LOS E. In that type of situation, a choice must be made: add capacity to the facility to achieve LOS E; or accept something worse than LOS E because the impacts associated with achieving LOS E would be too great and counter to the vision for the place. In the end, it is a choice that planners, designers, and local leaders must make.
Efforts to improve LOS for one mode may impact the LOS of other modes negatively. Ultimately, it is the type of place and its modal characteristics that determine the outcome of the competing LOS interests. Where pedestrian mobility is a priority, such as within a downtown area, the LOS for pedestrians, bicycles and transit should be prioritized over that for automobiles.
Along highways and rural routes, the LOS for cars will be a priority and along urban arterials, where the quality and safety of travel for many modes is necessary, the LOS for all modes must be carefully balanced. The solution for any place must reflect the vision and goals for that place, as determined collaboratively by the stakeholders. Long-term plan resolution is vital to the successful development of the ultimate vision.
Characteristics affecting LOS for Office Employment Areas:
- There is a significant spike in traffic congestion, pedestrian presence, and transit use during morning, lunchtime, and evening rush hours
In office employment areas, employees generally arrive and depart during concentrated periods - in the morning and evening, and a lesser concentration during the lunch hour as employees travel to restaurants or to run errands.
The rush hour peaking characteristics experienced in office employment areas require that planners and designers have a clear understanding of the travel patterns during those time periods (both currently and in the future, taking planned development into consideration).
To be considered great streets, office employment corridors must provide safe and efficient bicycle, transit and pedestrian facilities to accommodate employees that commute to work via bus or light rail and then walk to their various places of employment. Planners, designers, and local leaders should strive to:
- Provide sidewalks that are continuous and wide enough to include pedestrian-friendly streetscape elements
- Maximize separation between pedestrians and motorized traffic
- Keep motor vehicle travel speeds as low as practicable
- Providetransit service that is frequent, reliable, and easily accessible
Bicycle commuting is environmentally responsible, reduces vehicular congestion, and is economically inexpensive for users. The following measures can be taken to encourage bicycling and enhance LOS in office employment areas:
-
Credit: CH2M HILL Maximize the outside travel lane width and provide clearly identifiable bike lane striping, as shown in the image at right. Bike lanes can also work well along corridors with designated transit lanes, because transit lanes are often relatively low-volume. - Direct trucks and other large vehicles to designated truck routes whenever possible to minimize conflicts with bicyclists.
- Keep motor vehicle travel speeds as low as practicable.
- Ensure that drainage grates are visible and bicycle friendly.
-
Credit: css.org Provide secure, visible bicycle racks to discourage theft, as shown at right. - Be vigilant about pavement maintenance and repair, especially in bike lanes; large potholes and cracks can be a serious hazard for bicyclists.
Despite the importance of providing a high LOS for pedestrians, transit users, and bicyclists, it is still critical to maintain an adequate LOS for motor vehicle travel. Many employees commute via automobile, and failure to provide safe and suitable vehicular operations could discourage employers from locating in the area. The needs of motor vehicles must be balanced with those of other modes of travel.
Widening a roadway to increase capacity and improve vehicular LOS detracts from the pedestrian, jeopardizes safety, and makes street crossing more difficult. Road widening can also exacerbate signal delay due to the increase in walk phase time required for pedestrians to navigate the intersection.
Dealing with traffic congestion is becoming an inescapable part of daily life in the St. Louis region, especially during the peak hour. Our daily travel patterns are shaped by social and professional structuresthat create substantial spikes or peaks during the morning and evening rush hour. Increasing roadway capacity enough to completely eliminate peak period congestion would be unreasonably expensive and have damaging effects on the surrounding residences and businesses. There are, however, measures that can be considered to improve vehicular LOS during peak conditions:
- Left-turning vehicles are one of the biggest intersection safety hazards. During peak hour periods, prohibiting problematic left turns, especially those presenting a substantive safety issue, can improve traffic flow and reduce the risk of crashes. If left turn prohibition is not an option, restricting left turns to a protected only, or green arrow phase will eliminate the increased crash risk associated with "permitted" left turns (allowing traffic to turn left at a green light when they find a gap in the opposing traffic stream).
- On-street parking is an important component of successful office/employment corridors; however, during the peak period it may be prudent to convert one row of parking into an additional travel lane to enhance roadway capacity.
- Encouraging staggered or flexible work hours at major business centers can help alleviate some peak hour congestion. Although not all industries are conducive to flexible employee schedules, those that are should consider the benefits of this strategy (and possibly even offer incentives for participation).
- Details
- Last Updated on Wednesday, 11 June 2014
Article
Design speed is the rate of travel for which the physical characteristics of a roadway are designed. The design speed for a given roadway plays a large role in determining the scale and design of roadway characteristics. For example, if a design speed of 35 mph is chosen for a given roadway, all aspects of its design, such as roadway curvature, lane width and intersection elements will safely accommodate vehicles traveling at 35 mph. Roadside design elements vary greatly with design speed, as fixed objects along the streets present a greater substantive safety risk at higher speeds.
Before discussing design speed, it may be useful to introduce and explain a few related topics:
- Operating Speed: a measure of the speed at which most drivers actually travel on a given arterial section under free flow conditions (often equated to the 85th percentile speed of traffic observed under free flow conditions). On urban and suburban arterial streets, operating speed is heavily influenced by the presence, spacing, and timing of traffic signals.
- Target Speed: the speed at which drivers should travel on a given arterial section. Ideally, a facility's target speed and posted speed should be the same.
- Posted Speed: the upper speed limit for a given arterial section; often commensurate with target speed. The posted speed often represents the desired target speed.
Designers and engineers often choose a design speed that is higher than the posted/target speed, which encourages vehicles to travel at speeds higher than the target speed, especially along lower speed corridors. A facility's design speed and target speed should be equal, to keep vehicular speeds at or below the desired target speed. All elements of the streetscape should be designed to support the target speed for the corridor.
In a multi-modal environment with significant pedestrian presence, it is essential to provide adequate vehicular stopping sight distance and intersection sight distance. It is good practice to use a relatively low design speed (e.g. 30 mph) but provide the equivalent of 40 mph of sight distance.
Functional Classification is traditionally used to determine the target speed for a given arterial street. Although roadway planners and designers should consider functional class when selecting the facility's posted speed, the characteristics of each individual place should be the primary consideration used in choosing a target speed. A keen awareness of an area's unique characteristics will prevent the misapplication of broad standards that may be inappropriate for the place.
Design Speed for Office Employment Thoroughfares
Characteristics that influence the choice of design speed in these place types:
- Design speed, target speed, and posted speed are the same;
- There is a significant pedestrian, bicycle, and transit presence; and
- Vehicles usually must reduce travel speeds before approaching office employment areas
Select the lowest practical target speed. As speed increases, so does the safety risk for pedestrians and bicyclists. Studies on this subject have correlated higher speeds with higher fatality rates for pedestrians when struck by vehicles. For place types such as these that have higher pedestrian and bicycle activity levels, reducing speeds is an effective way to improve safety. Selecting the lowest practical target speed creates the safest environment for pedestrians, provides easier access to/from abutting land uses, and eases the transition between modes of travel. Ideally, an office employment area would have a target speed of 25 mph, especially if bicycle commuting is to be an attractive choice for employees. The maximum target speed for this thoroughfare is 30 mph. "Group A" cyclists may be comfortable alongside higher speed traffic, but lower speeds are essential in order to encourage the broader population to participate in bicycle commuting.
Lower speeds also make it easier for drivers to perceive conflicts on the road ahead and react accordingly. Drivers require less time and shorter distances to stop or slow down to avoid conflicts in low-speed environments. Conflicts on the street are numerous along office employment thoroughfares due to vehicles entering or exiting the street from adjacent access points; pedestrians unexpectedly entering the traveled way; vehicles stopping to park or pulling out of parking stalls; buses pulling over at a stop or pulling out from a stop; and other vehicles unexpectedly changing lanes in congested conditions.
There is often a misperception that slow speeds result in slower travel times along a given arterial street. The travel time along arterials, however, can only be as fast as the intersections (particularly the signalized intersections) allow. High posted speed limits will do nothing to improve arterial travel time if there is significant delay experienced at the intersections. In fact, slower speeds along an arterial can contribute to improved overall travel times by allowing more time for better progression and coordination between signals. Given the propensity of many commuters to drive as fast as they can on their daily commutes, it is imperative that coordinated signal timing be consistent with the target speed. Commuters are usually intimately familiar with their travel routes, and they will often drive faster than they should if they know that by doing so it will allow them to pass through the next light. Signal coordination that encourages speeding between signals to "hit the green" before it goes red should absolutely be avoided.
For vehicles attempting to gain access from adjacent land uses and crossroads onto the respective thoroughfare (or vice versa), identifying an opening in the traffic stream to safely enter, exit, or cross (commonly referred to as gap selection) is of paramount importance. Drivers must be able to accurately assess whether an opening is acceptable in order to safely navigate to and from the arterial. As speed increases, the number of acceptable gaps decreases and it becomes increasingly difficult for drivers to identify safe gaps. Selecting the lowest practical design speed for a corridor will maximize the ability of drivers to effectively assess gap acceptability, and as a result, safely enter and exit the arterial traffic stream.
Consider Rush Hour Speed Reductions. Most office employment places experience "rush hour" or "peak hour" pedestrian and bicycle congestion at the beginning and end of the day when employees are arriving or departing. Lunch time can also present peak pedestrian levels if the office employment area has restaurants and commercial services within walking distance. These spikes in pedestrian activity increase the conflicts along the thoroughfare. Low speed vehicular traffic is imperative during these times to provide the safest possible environment for all users. Special speed limits for these time periods should be considered as a method of further prioritizing pedestrians, bicyclists, and transit. Clear and visible signing is vitally important when choosing to reduce speeds in this manner.
Support speed transitions with design elements. It is important to consider and plan for any speed transitions that may exist beyond a given area. Appropriate signing, traffic calming measures, and enforcement are essential to ensure safe speed transitions. This is particularly important in office employment areas where the posted speed increases significantly beyond the place.
Enforcement is an effective measure, but long-term efforts can be costly. Studies have shown that when enforcement measures are removed, vehicles typically resume higher travel speeds. One measure that has proven effective in Minnesota is the use of speed limit signs in conjunction with radar speed measurement displays (see Driver Speed Awareness PDF). Although they are not appropriate in all locations, speed measurement displays are particularly beneficial in areas that are plagued by speeding motorists.
Design for the target speed. Once the target speed is set (and consequently the design speed and posted speed), controlling roadway elements must be carefully designed to support travel at the desired speed. The target speed limit will become meaningless if lane widths, horizontal clearance, median type and width, and other features are inconsistent with the posted speed limit. ITE's Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities identifies the following design elements that should be considered when lower speeds are desired:
- Select narrow lane widths. Selecting narrower lanes helps to reduce travel speeds, and conversely, lanes that are excessively wide contribute to higher speeds. There is a growing body of research regarding the correlation between lane width, speed, and substantive safety. The latest research suggests that for travel speeds equal to or less than 35 mph, there is no difference in substantive safety performance between lane widths of 10', 11', and 12'. In other words, lane width has little effect on substantive safety in low-speed environments, such as office employment places. Site-specific characteristics will influence the decision between 10', 11', and 12' lanes. Additionally, narrower lanes also leave more right-of-way available for the areas "beyond the pavement", such as sidewalks, tree plantings, building frontages, etc. Converting a 4-lane section with 12-foot-wide lanes to 10-foot-wide lanes will provide a net gain of 8' in additional right-of-way for other uses.
- Eliminate superelevation in horizontal curves. If horizontal curves are present along the thoroughfare, superelevation, or banking of the roadway through the turn, is not recommended as it can encourage higher speeds.
- Eliminate shoulders. Here again, the narrower travel way can have a traffic calming effect, which should provide a safe environment for bicycles to share the travel lane with vehicles. Right-of-way in office employment areas, beyond the travel lanes, is best used for improved facilities for pedestrians, transit and bicycles.
- Include on-street parking. The presence of on-street parking has traffic calming effects, contributing to the desired lower-speed environment. Parking movements tend to calm traffic and the presence of parking cars, once again, has a narrowing effect on the travel way, ultimately contributing to slower speeds. On-street parking also provides a buffer between vehicular traffic and the pedestrian realm.
- Use curb extensions when appropriate. Particularly at pedestrian crossings and intersections, curb extensions as shown at right, can also contribute to narrower streets and slower speeds. Curb extensions also increase visibility between pedestrians and vehicular traffic. Coordination with emergency services is important to ensure that curb extension design accommodates larger vehicles such as fire trucks.
-
Minimize intersection curb return radii. The size of the radii for the curb returns at intersections has a direct impact on vehicular travel speed in these areas.
Smaller radii encourage slower speeds. Care should be taken, however, to ensure that school buses and transit buses are accommodated at key locations.
When channelized right turns are chosen, care should be taken to ensure that the geometry of the right turn does not encourage higher speeds.
- Increase awareness of bicycles and pedestrians. Pavement treatments that delineate and highlight sidewalks, crosswalks and bicycle lanes, increase driver awareness of their presence. Textured materials and pavers, colored concrete or asphalt, and pronounced striping can effectively highlight pedestrian, bicycle and transit facilities and consequently discourage higher travel speeds. This is vitally important if bicycling is to be viewed as an attractive commuting choice.
- Post clear signage. Clear and concise signs along the street are vital in communicating the speed limit to vehicular drivers. See the signing section of this manual for more information.
- Details
- Last Updated on Wednesday, 11 June 2014
Article
Traditional Philosophy
The St. Louis region contains a number of individual streets and street types, each serving a different purpose within the transportation network. A functional classification system is used to group and describe roads according to the type of service they provide and their role in the network.
The functional classification for a given roadway is determined based on its setting (urban or rural) and whether its main role is providing connectivity, mobility, or accessibility. The number of vehicle miles traveled (VMT), average annual daily traffic (ADT), and abutting land uses of a roadway are also considered. Traditionally, the roadway functional classification system has been used to describe how travel flows through the regional roadway network and to determine project eligibility for inclusion in the Long Range Plan and short-range Transportation Improvement Program (TIP).
East-West Gateway, the metropolitan planning organization (MPO) and council of governments (COG) for St. Louis, is responsible for maintaining and updating the region’s functional classification system. To maintain the functional classification system, East-West Gatewayaccepts applications for functional classification revision during the months of May and November each year. A system-wide review is conducted every 3-5 years.
Table 1, at right,depicts the region’s traditional functional classification system. The classes that are most applicable to the St. Louis Great Streets Initiative have been shaded yellow.
A portion of a typical urban/suburban network is shown in the figure below. The arterial streets form the backbone of the network.
Local roads feed the collectors, which in turn feed the arterials.
This example is similar to many of the arterial networks throughout the St. Louis region.
Traditional planning and design standards classify the functionality of highway and street networks based on two major factors:
-
access to adjacent properties and land uses; and
-
mobility for vehicles needing to travel through the area without stopping at adjacent developments.
In this traditional approach, the exhibitbelowis often used to illustrate the relationship between access, mobility, and the street network.
The prevalence of this well-known figure and the concepts it illustrates help explain, at least in part, why some of our arterial streets are unwelcoming to pedestrians and provide poor access.
Arterials are often characterized as facilities designed to transport people and goods and provide mobility.
While freeways and expressways within the principal arterial system (such as I-64 or I-170) are intended to move people and goods quickly and efficiently, the other principal arterials and minor arterials in the transportation network are not intended for this purpose.
Minor arterials which are designed or function more like freeways present a major problem for the St. Louis region.
For example, facilities like Watson Road, Olive Road, Manchester Road, and Lindbergh Boulevard carry the majority of the metropolitan area’s traffic volume.
Balancing the need to provide access and mobility along many of these arterial streets is one the greatest challenges facing municipalities, local agencies, and communities in their efforts to create great streets.
New Philosophy
In Chapter 4 of the ITE publication Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities, streets and highways are classified according to traditional functional classification and what is referred to as “thoroughfare type.” This additional classification scheme is used with the recognition that functional classification alone does not adequately describe the character and adjacent land uses of an arterial street. The categorizations used in the functional classification system are too broad to reflect the true character of an arterial street or capture differences between roadway segments.
The ITE publication uses the term “major thoroughfare” to describe major urban or suburban multimodal streets (typically arterials or collectors) that are designed to support and complement adjacent land uses. As the regional bus and light rail systems continue to expand and gain ridership, major thoroughfare design considerations will be increasingly relevant in St. Louis.
Major urban thoroughfares are divided into two main types:
- Walkable, pedestrian-oriented urban streets serving small, mixed-use developments
- Auto-oriented, mobility-focused streets serving single-use developments
The ITE publication predominantly focuses on the first of the two categories noted above; however Chapter 11 discusses some of the key considerations for mobility-priority streets.
The tableat rightillustrates the relationship between traditional functional classification categories and thoroughfare types. In light of these relationships,the Great Streets Initiative focuses on the following thoroughfare types:
-
Boulevards: divided arterials in urban and suburban environments; can be high speed (40-45 mph) or low speed (35 mph or lower). Typically serve as primary routes for goods movement and emergency response.
- High speed boulevards are mobility-priority corridors emphasizing traffic movement over longer distances, with very few access points. Adjacent land uses are typically larger single-use parcels with sizeable, landscaped setbacks.
- Low speed boulevards are walkable, multimodal corridors providing relatively few access points (but still more than high-speed boulevards). These roadways are often transit corridors with high ridership.
- Avenues: low- to medium-speed arterials and collectors; shorter in length than boulevards with more access provided. These thoroughfares are typically walkable, with a heavy emphasis on pedestrian and bicycle travel.
-
Streets: low-speed minor arterials and collectors that focus on access to adjacent land uses. These roadways are often the “main streets” of commercial or mixed-use areas, with parking provided along the curb.
Table 3 below outlines the primary thoroughfare types applicable to the place types discussed in this guide. These recommendations are intended as general guidelines; because every community is unique, there is no one-size-fits-all rule for thoroughfare type selection.
Given the need to use functional class and thoroughfare type to describe roadway characteristics, this guide will use the following categorizations to define the various elements of the arterial street.
Functional class will be used to define:
- The arterial’s role in the regional network
- Type of freight service provided
- Type of transit service provided
Thoroughfare type will be used to define:
- Roadside characteristics and treatments
- Traveled way elements
- Intersections
The ITE guide indicates that a road’s functional classification should dictate its design speed. Because many of the arterial streets in the St. Louis region have a functional classification that would prescribe an inappropriately high design speed under such an approach, this guide recommends that design speed be determined based on place-specific characteristics and the community’s vision for the particular place. The use of these alternative criteria would likely result in speed reductions for certain segments of the arterial.
When determining design speed, the road’s functional classification may be an appropriate starting point, but it should not be applied without considering a number of other important factors.
- Details
- Last Updated on Wednesday, 11 June 2014
Article
Successful great streets should produce transportation and land use solutions that are both safe and feasible, while at the same time balancing other community values. Above all else, the public values safety and expects that transportation agencies will only implement solutions that provide an acceptable level of safety. The geometric design for a thoroughfare should properly reflect safety for all modes of travel. It should do so within the context of a host of constraints and considerations, including the type of place, land use features (both existing and planned), roadside and community effects, and cost considerations. Consider the images below - where would you feel safer walking?
Safety is a broad term and can have a variety of meanings depending on the setting.
In the world of great street planning and design, two types of safety are often referred to: nominal safety and substantive safety.
- Nominal safety is a thoroughfare's relative ability to comply with standards, warrants, guidelines,and sanctioned design procedures.
- Substantive safety is the actual crash frequency and severity for a giventhoroughfare for all modes of travel.
For great streets, we are most interested in the issue of substantive safety. A great street design element should not necessarily be deemed unsafe simply because it does not comply with a particular standard or guideline. While noncompliance can be an issue, a thoroughfare's substantive safety - its "track record" - is a more fundamental consideration and is based on actual performance at a specific location.
When we talk about substantive safety for great streets, we are talking primarily about the crash risk that exists for all modes of travel: vehicular, pedestrian, bicycle, and transit. Great streets must provide environments in which all of these users can operate safely, without risk (or fear) of being involved in a crash. There are two very important great street characteristics to point out in this regard:
-
High pedestrian presence is a hallmark of most great streets. In order to encourage such presence, the place must provide a safe environment for these users.
-
Vehicular travel speed must reflect the desire for pedestrian safety. There is a direct correlation between high speeds and pedestrian safety. As speeds increase, crashes involving pedestrians are more severe.
Safe travel for all modes is a key objective in the St. Louis region. The East-West Gateway Council of Governments, the State of Missouri, the State of Illinois, and a number of other agencies are increasingly recognizing the importance of safe travel. In 2004, East-West Gateway spearheaded a major initiative under the banner “Someone’s Future is in Your Hands: Travel Safe.” The campaign is a component of regional and national efforts to reduce the number of driver and pedestrian traffic deaths.
- Details
- Last Updated on Tuesday, 10 March 2015
Article
Our transportation network is a regional system. It consists of streets, sidewalks, light rail lines, bicycle lanes, and all other infrastructure that is in place to support the movement of people and goods. The focus of this project is our streets and how to think differently about their development. This cannot be done, though, without also considering the broader transportation network of which our streets are a part.
From a purely vehicular perspective, there is a hierarchy of streets in our transportation system. Traditionally, the roadway functional classification system has been used to describe how travel flows through this hierarchy. East-West Gateway, the metropolitan planning organization (MPO) and council of governments (COG) for St. Louis, is responsible for maintaining and updating the region’s functional classification system. The table at right depicts the current regional classification system.
The table above is based primarily on vehicular travel. Great streets, though, are more than just conduits for vehicular traffic.
They are public places woven through the social and economic fabric of our communities. In this context, the street network is much bigger than the travel lanes that carry automobile traffic through our region. It is a complex system of dynamic components that dramatically affects the quality of our public spaces. If our street network is only a conduit for automobiles, then we are failiing to maximize the massive investment of public revenue into our transportation infrastructure. This principle is at the core of great street planning and design.
Great streets must be "complete". They must move vehicular traffic, yes; but that is only one of many important roles that they can and should have. They should provide access to all users, regardless of economic status or disability. They should stimulate economic growth. They should offer multiple, attractive modes of travel from which to choose. They should provide attractive places for the congregation of local residents and visitiors. For streets to be great, these factors and many others must be considered as we choose how to allocate space along our thoroughfares.
Space Allocation is a Choice. Historically, the automobile has dominated space along most of our thoroughfares. Growing populations with growing numbers of personal automobiles-per-household have caused us to choose thoroughfares that are good for little else than the movement of vehicular traffic. To make matters worse, when congestion rises along these thoroughfares we have typically chosen to add vehicular capacity by widening the travel way. The result of these choices is a network of thoroughfares that is predominantly unfriendly to pedestrians, transit, and bicyclists. It has also negatively affected land uses along our thoroughfares.
If we want to create great streets in place of these auto-dominated roadways, we must think differently about space allocation along the thoroughfare. Space allocation is a choice, and our choices have consequences. Choosing to prioritize vehicular traffic will often have negative consequences for other modes and abutting land uses. Choosing to prioritize other modes is a healthy part of great street development, but it may negatively impact vehicular mobility along the thoroughfare. This is where the street network is an extremely important consideration in great street planning and design. Choices that may constrain vehicular travel, such as road diets, lower speeds, raised medians, etc., can be offset if the surrounding street network is effectively utilized.
Road diets must consider network context. All of the streets within the regional system work together to provide mobility and access throughout the metropolitan area. Every street serves a specific function within the regional network. This is an important point to remember during the planning phases of great street development. If road diets are considered, the following questions should be addressed in evaluating its merits:
- Does the existing road serve a major mobility function in the region?
- If so, are their parallel streets nearby to help serve potential excess traffic demand?
- If the parallel street system is severed/discontinuous, could improvements to the local road network mend those gaps to provide alternative route choices for excess traffic demand?
- Is there a desire/opportunity to promote transit along the thoroughfare in order to serve excess traffic demand?
- Is there a desire to provide good bicycle accommodations?
Grids are important for great streets. Regardless of whether a road diet is part of a great street development, the street network surrounding the respective thoroughfare is an important component to consider in the decision making process. At the dawn of the street system in America, urban areas typically developed in a "grid pattern". Over time, suburban sprawl led to non-grid development patterns in many areas, resulting in disconnected networks that rely upon select major arterial streets for the vast majority of vehicular mobility.
Transforming these thoroughfares into great streets is a complex challenge, and it is further complicated by the lack of grid network surrounding the respective corridor. If great streets are desired in such locations, be sure to examine the surrounding street network for opportunities to improve connectivity. Sometimes it may be as simple as opening a cul-de-sac to connect with a nearby street. In other cases, more substantial links may be required; but the increased network capacity can allow us to think differently about space allocation along the thoroughfare in question. It may suddenly be reasonable to reduce vehicular capacity along the thoroughfare if network capacity can be improved through enhanced connectivity. A reduction in vehicular capacity along the thoroughfare gives us more freedom in how we choose to allocate space and prioritize other modes.