Level of Service

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 the PDFs 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.  The City of Charlotte also provides guidance on inclusion of multimodal factors that influence vehicular LOS.

Credit: Charlier Associates, Inc.

Pedestrians

Pedestrian LOS is determined by the following factors:

• Existence of a sidewalk along the arterial
• Amount of lateral/horizontal separation between pedestrians 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.

Credit: TRB TCQSM

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.

Credit: css.org

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 capacity and 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 of how development will affect future traffic.  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 Guide suggests 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 Level of Service for Commercial/Service Corridors:

• Referred to as "mobility-priority areas" in ITE's Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities (see Chapter 11)
• Adjacent land uses are typically low-density, large-site commercial, industrial, or service developments
• Large trucks are common
• Large parking lots and/or garages create conflicts between access and mobility along the arterial street

Commercial/Service corridors are often high-volume arterials; therefore, accommodating and encouraging pedestrian, bicycle, and transit use while maintaining efficient vehicular operations can be challenging.  However, providing facilities for these modes can help reduce vehicular demand and improve level of service.  To accommodate and encourage pedestrian traffic, planners, designers, and local leaders should aim 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
• Provide pedestrian signals, over/underpasses, and walkways
• Provide frequent bus service and safe pedestrian facilities to encourage transit use

Credit: css.org

To encourage bicycle travel, commercial and service corridors should also include safe, efficient bicycle facilities.  Bicycling is an environmentally responsible and economically practical choice.  The following measures can be taken to enhance bicycle LOS along these corridors:

• Maximize the width of the outside travel lane and provide bike lane striping that is clear and visible, as shown in the image at right.
• Route trucks and heavy vehicles to designated routes to minimize conflicts with bicyclists.
• 

  Credit: css.org

  Keep motorized speeds on the street as low as practicable.

• When drainage grates are required, make sure they are highly visible and bicycle friendly.
• Provide bike racks that are secure and visible to discourage theft, as in the image at right.
• Regularly maintain the pavement and repair potholes and cracks, which are significant hazards for bicyclists.

Parking may be provided and accessed along commercial and service corridors via numerous access points serving smaller parking lots or fewer access points serving large lots.

Providing numerous access points increases the number of potential conflicts and crashes along the arterial.  Providing fewer access points into larger parking lots reduces the number of access points, but the demand for each increases.  Each of these access points functions more like an intersection than a driveway, and may even need to be signalized.  These access points and intersections must be designed to minimize delay on the arterial.  The presence of large trucks along these corridors will largely influence intersection design, namely curb return radii, left turn lane storage requirements, and right-turn channelization.  See the Intersections section of this guide for more information.

Despite the importance of providing a pedestrian-, transit-, and bicycle-friendly environment, it is still critical to maintain an adequate LOS for motor vehicle travel.  Arterial streets through commercial and service corridors typically serve high volumes of vehicular traffic, and failure to provide safe and suitable vehicular operations could discourage employers from locating in the area.  As provisions for safe vehicular operations are considered, it is important to remember that the needs of motor vehicles must be balanced with safe, efficient operations for the other travel modes.

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 structures which create substantial spikes or peaks during the morning and evening rush hour.  Increasingly 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).
• Signal timing and phasing should account for the fact that large trucks, which are often present along these corridors, take longer to accelerate from the stopped position than smaller vehicles. Signals should be timed and phased to minimize delay.
• If on-street parking is provided along the corridor, eliminating the peak direction parking lane during rush hour can provide an additional through lane for increased vehicular capacity.

Resources

PDFs:

• MO Practical Design Guide
• FDOT LOS Tables
• FDOT Quality/Level of Service Handbook
• ITE Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities (See Chapter 7)
• TCQSM 3rd Ed Chapter 2 - Mode and Service Concepts
• TCQSM 3rd Ed Chapter 4 - Quality of Service Concepts
• TCQSM 3rd Ed Chapter 5 - Quality of Service Methods
• TCQSM 3rd Ed Chapter 7 - Demand-Responsive Transit
• TCQSM 3rd Ed Chapter 11 - Glossary and Symbols

Links:

• TRB Transit Capacity and Quality of Service Manual
• ITE Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities, Chapter 7
• FHWA Flexibility in Highway Design, Chapter 4 Design Controls
• Massachusetts Design Guide, Chapter 3 Design Controls
• The Brookings Institution Policy Brief # 128
• FDOT Systems Planning Office

Other References:

(not currently available in electronic format) 

• AASHTO Green Book, Chapter 7, pg. 470 (2004 Edition)
• ITE Traffic Engineering Handbook, Chapter 4 (1999 Edition)
• TRB Highway Capacity Manual, Chapters 10, 15, and 16 (2000 Edition)