Level Of Service Analysis

Traffic Engineering

By: Jared Norsworthy

Submitted: 12/9/14

Objective:The purpose of this study was to conduct a level of service analysis of four

different intersections and compare the results.

Introduction: Determining the level of service of a road is an important aspect when considering how often drivers, bicyclist, and pedestrians use these roads. This is also reflected in the “NCHRP-Multimodal Level of Service Analysis for Urban Street: Users Guide” when it states that, “[The] level of service is used to translate complex numerical performance results into a simple letter grade system representative of the travelers’ perception of the resulting quality of service provided by the facility.” By taking the travelers perspective of the quality of the roadway, traffic engineers are able to gain a better understanding of changes that may need to be made to an existing road so that the quality of the traffic being moved through an intersection is better. As referred to in the NCHRP excerpt, numerical data is required in order for the grade of the road to be developed.

A List of this numerical data can be viewed in, ”Traffic Level of Service Analysis Guidelines”. Examples of these types of numerical data are

Traffic Volume Data: The number of drivers, bicyclist, and pedestrians that go through an intersection during a designated time interval.

Intersection Geometry: Determined in condition diagrams, provides number of lanes, lane widths, cross walk lengths, etc.

Signal Timing: The length of time in which the signal is green, yellow, or red.

Although the numerical data is essential to conducting a level of service analysis, some non-numerical pieces of data that are needed as well are

Signal Type: Is the intersection unsignalized, pretimed, or based on the time of day.

Lane Functions: whether turning left or right is permitted or the direction the lane takes drivers.

It is because of these pieces of information that accurate assessments of the level of service of a road can be determined.

Scope:

The level of service analysis was conducted at the following intersections V Street NW and 10th Street NW V Street NW and 11th Street NW U Street NW and 11th Street NW Florida Avenue NW and 11th Street NW

The numerically name streets all run north and south while the other streets run east and west. Both intersections on V Street NW are unsignalized and rely on stop signs in order to control the flow of both pedestrians and vehicles. The intersections of U Street NW and Florida Avenue NW are signalized and rely on traffic and pedestrian signals to

control the flow of traffic. All four intersections are 4-way intersections that all have designated crosswalks for pedestrians to safely travel in. 10th and 11th Street NW both contain one lane that runs north and one that runs south. Florida Avenue NW and U Street NW both have two lanes that are travel east and west. V Street NW however, has one lane running just east.

Figure 1: The intersection V St. Nw and 10th St. Nw

V St. Nw

10th St. Nw

Figure 2: The intersection V St. Nw and 11th St. Nw

V St. Nw

10th St. Nw

Figure 3: The intersection U St. Nw and 11th St. Nw

11 St. Nw

U St. Nw

Figure 4: The intersection Florida Ave. Nw and 11th St. Nw

Methodology and Data Collection:In order for a level of service analysis to be done, information from

previously conducted studies need to be used. The geometry of the intersections needed to be determined and this was done during the “Condition Diagram Study.” Next the traffic data needed to be collected for each intersection and this was completed when the “Intersection Turning Movement Counts Study” was done. The last piece of information need was the signal times and phases which were completed in the “Signal Timing and Phasing Study.” Once all of these studies had been conducted the information was then put into both HCS and Synchro programs to be analyzed.Analysis of Data:

11th St. Nw

Florida Ave. Nw

V Street NW and 10th Street NW HCS

V Street NW and 10th Street NW Synchro

V Street NW and 11th Street NW HCS

V Street NW and 11th Street NW Synchro

U Street NW and 11th Street NW HCS

U Street NW and 11th Street NW Synchro

Florida Avenue NW and 11th Street NW HCS

Florida Avenue NW and 11th Street NW Synchro

HCS Level of Service Grade

Synchro Level of Service Grade

V Street NW and 10th

Street NWA A

V Street NW and 11th

Street NWA A

U Street NW and 11th

Street NWNorth/South – C/CEast/West – B/BPedestrian – BBicyclist - A

North/South – B/BEast/West – B/B

Florida Avenue NW and 11th Street NW

North/South – C/CEast/West – B/BPedestrian - BBicyclist - A

North/South – B/CEast/West – B/A

From the data above, the level of service for each intersection was

determined. For both of the unsignlaized V Street NW intersections, HCS and Synchro determined the level of service grade to be A’s. For the signalized intersections, HCS determined that the intersections had the same level of service. However, for Synchro, the U Street NW intersection had a level of service of a B for both the north/south and east/west directions. For the Florida Avenue NW intersection, Synchro determined the level of service to be a B for the northbound, C for southbound, B for eastbound, and an A for westbound.

Conclusion and Recommendations: The level of service for each intersection was determined as accurately as possible. HCS gave the unsignalized intersections the same grade and the signalized intersections the same grade as well. However Synchro only gave the same level of service grade to the unsignalized intersections and determined that the level of service for the signalized intersections was different. Another observation that was noticed was that for the signalized intersections, the HCS program broke down the data more thoroughly into sections for roads, for drivers, pedestrians and bicyclist, while Synchro only determined the level of service for the drivers.

References

1. http://www.pmcworld.com/client/sunnyvale/documents/4-11-11/Traffic-Level-of-Service-Analysis-Guidelines.pdf

2. http://www.reconnectingamerica.org/assets/Uploads/nchrp_w128.pdf