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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 maximum quantity of traffic that could move 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 multi-modal factors that influence vehicular LOS.
Redmond example
Credit: Charlier Associates, Inc.

Pedestrians

Pedestrian LOS is determined by the following factors:

  • Existence of a sidewalk along the thoroughfare
  • Amount of lateral/horizontal separation between pedestrians and motorized traffic
  • Volume of motorized traffic on the thoroughfare
  • Speed of motorized traffic on the thoroughfare

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 service, street-running light trail transit 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 thoroughfare
  • Speed of motorized traffic on the thoroughfare
  • Amount of heavy vehicles/trucks on the thoroughfare
  • 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

There are two major areas of interest related to vehicular LOS:

  • Intersections: Quality and level of service at intersections control the overall quality and level of service for the broader thoroughfare. 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 thoroughfare 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 roadway, although as noted above, the efficiency (or lack thereof) of the intersections will control the capacity and LOS of the thoroughfare as a whole. As with intersections, street segment evaluation methods are traditionally focused on vehicular LOS. The City of Charlotte provides good guidance that accounts for multi-modal needs along the thoroughfare. 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 thoroughfare. 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, not a mandate. The nature of the thoroughfares 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 thoroughfare, 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.

Level of Service for Downtown Main Streets:

Characteristics affecting level of service (LOS) for Downtown Main Streets are:

  • Significant pedestrian presence
  • Significant transit presence
  • Traffic congestion is more tolerable
  • Low vehicular speeds are desirable

High pedestrian and transit presence in downtown areas requires that we prioritize LOS for those users above LOS for those in cars. Great streets in downtown areas must first and foremost provide safe and efficient use for pedestrians and transit. To do so, planners, designers, and local leaders should focus on the following pedestrian measures:

  • dwntnsidewk
    Source: CH2M Hill
    Provision of sidewalks that are continuous and wide enough to provide the types of desired pedestrian services, as shown in the image at right;
  • Maximize the amount of lateral/horizontal separation between pedestrians and motorized traffic;
  • Keep motorized speeds on the thoroughfare as low as practicable; and
  • Transit service that is frequent, reliable, and easily accessible.

An important byproduct of thoroughfares designed with high LOS for pedestrians and transit is bicycle accessibility. When automobile travel speeds are slowed, bicycles can usually rely on safe and efficient travel while sharing vehicular travel lanes. Signing and parking design can further improve the environment for bicycles along downtown main streets.

Vehicular LOS must also be considered for downtown areas, as indeed many pedestrians travel to the area by car, making access a priority over mobility through the downtown. The LOS measures of average travel speed and delay can therefore be more flexible since slower speeds are more desirable.

As provisions for safe vehicular operations are considered, it is important to remember that congestion is not necessarily bad and is often unavoidable at peak travel times.

Slower speeds and somewhat longer delays at intersections offer several important benefits to downtown main streets:

  • Lower speeds create a safer environment for both pedestrians and motorized vehicles because drivers have more time to perceive and react to potential conflicts.
  • LOS 10
    Credit: CH2M HILL
    Lower speeds can also allow better progression between signals if the signals are located and timed properly (see the Intersections section of this manual for more details)
  • Vehicular delay at intersections is in part a result of allowing sufficient time for pedestrians to cross the street. This is a tradeoff worth making along downtown main streets, as in the image at right.

Adding vehicular capacity, in an attempt to improve vehicular LOS, through roadway widening makes street crossing for pedestrians more difficult and less safe.

Signal delay will usually increase under such widening due to the increase in walk phase time required for pedestrians to navigate the intersection. Additionally, a higher LOS for transit, pedestrians and bicycles offsets the impacts of lower vehicular LOS by providing many options for travel to and through a downtown area.

Congestion is a reality for most downtown areas, including the downtown areas in the St. Louis region. Social and professional structures contribute to significant spikes in daily travel during the morning and evening rush hour. It is neither feasible nor desirable to design for the elimination of congestion. There are, however, measures that can be considered to improve vehicular LOS during peak conditions:

  • One of the biggest conflicts at intersections is that of left-turning vehicles (from major onto minor street). During peak hour traffic, prohibition of left turns that are particularly problematic (as determined by safety data) can improve traffic flow and improve safety. If left turn prohibition is not an option, restricting left turns to a “protected only” phase (when opposing traffic is stopped as vehicles are given a green left turn arrow) will eliminate the increased crash risk associated with “permitted” left turns (allowing traffic to turn left when they find 'an acceptable gap' in the opposing traffic stream).
  • On-street or curb parking, as shown at right, is an important element of successful downtown main streets.
    Curb Parking
    Credit: CH2M HILL
    During peak hours, though, consideration can be given to elimination of the “peak direction” parking lane to add an additional through lane for increased vehicular capacity and improved LOS.
  • Encouraging staggered or flexible work hours at major downtown 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).

Current practice at the national level is starting to rely less on LOS as a measure of effectiveness. This is not to say that LOS is not important, but rather that there are other factors that must be considered when evaluating the quality or level of service provided. One such factor is that of "reliability" of the street for travel purposes. Does the thoroughfare operate in a consistent manner from day to day and in the peak conditions? If so, then users of the larger regional network can plan their trips accordingly.

For example, a commuter in the Central West End who needs to travel to Ladue might consider taking Delmar Boulevard through University City.

Reliability
Credit: CH2M HILL

However, the traveler must consider the typical conditions on Delmar if travel time is important. Knowing that Delmar is usually congested in "The Loop" area, the user will likely choose an alternate route such as Forest Park Parkway to avoid the congestion often present in the Loop. Regular congestion on Delmar through University City actually helps users make better choices about travel patterns. If the congestion was less predictable, the choice would not be as clear and users might be frustrated at the lack of reliability.

Resources

PDFs:

Charlotte Urban Street Design Guidelines:

Links:

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)