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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 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.
Redmond example
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 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.

Transit LOS
Source: 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.

Bicycle LOS
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 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 Level of Servicefor Residential Neighborhoods:

  • Significant pedestrian presence
  • Low vehicular speeds are desirable

Although the needs of motor vehicle trafficmust be considered, LOS for pedestrians and transit must often take priority along downtown main street corridors. To accommodate and encourage a significant pedestrian presence, 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 bus service that is frequent, reliable, and easily accessible

Although creating a safe, pleasant pedestrian environment is a high priority in residential areas, it is still important to provide an adequate level of service for vehicular travel. As provisions for safe vehicular operations are considered, it is important to remember:

  • Lower travel speeds create a safer environment for pedestrians and motorized vehicles because drivers have more time to recognize and respond to potential hazards
  • Lower speeds help create a quieter, more "livable" environment for residents and pedestrians along the street

Widening a roadway to increase capacity and improve vehicular LOS detracts from the pedestrian experience, 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.

Residential areas should prioritize access and focus less on mobility. The character of residential areas, with numerous parcels along the street, often necessitates the provision of more access points. Because slower speeds are desirable in residential areas, the LOS measures of average travel speed and delay can be applied with more flexibility.

Roundabouts can be an effective means of reducing intersection delay in low-speed residential areas. See the Intersections section of this manual for more information about roundabouts and intersection design.

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. 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).
  • On-street or curb parking can be used effectively along residential arterial streets; however, during the peak period it may be prudent to convert one row of parking into an additional travel lane to enhance roadway capacity.