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Conditions and Performance Report. Chapter 4

Conditions and Performance Report
Chapter 4—Operational Performance

Conditions and Performance Chapter Listing

Conditions and Performance Home Page


Introduction

Summary


Highway Operational Performance

Transit Operational Performance

 

Summary

Exhibit 4-1 highlights the key highway and transit statistics discussed in this chapter, and compares them with the values from the last report. The first data column contains the values reported in the 1997 C&P report, which were based on 1995 data. Where the 1995 data have been revised, updated values are shown in the second column. The third column contains comparable values, based on 1997 data.

Exhibit 4-1. Comparison of Operational Performance Statistics with those in the 1997 C&P Report

To examine highway operational performance, this chapter looks at daily travel per lane-mile, peak-hour volume/service flow ratio, and daily delay.

DVMT per lane-mile is the most basic measure, since it is a count-based metric. This measure increased at a faster annual rate on the Interstates than any other segments of the highway system between 1987 and 1997. DVMT per lane-mile increased at an annual rate of 3.40 percent on rural Interstates and by 2.00 percent on urban Interstates. Increased travel has not yet saturated rural highways to the degree it has impacted urban highways, so it has not resulted in similar congestion patterns.

Another way to examine highway congestion is to determine the percentage of peak-hour urban traffic that operates at a volume service flow (V/SF) threshold of 0.80 or higher. Between 1993 and 1997, congestion increased somewhat on urban Interstates while decreasing on other freeways and expressways and other principal arterials. The proportion of peak-hour travel exceeding the 0.80 threshold on urban Interstates increased slightly from 52.6 to 53.3 percent. On all urban principal arterials, it was 40.2 percent in 1997, down from 40.9 percent in 1995. Overall the congestion trends seem to have flattened over the past several years.

Daily delay is a more recently adopted measure of congestion, and is an attempt to use a measure that is readily observed by the traveling public. However, the delay values used in this report are modeled values, not directly observed values. Delay is expressed in terms of hours per thousand vehicle-miles traveled. Between 1993 and 1997, the greatest delay has been on "other principal arterial" highways in urbanized areas with more than 200,000 residents. These are higher-level roads that are accommodating significant metropolitan growth; the delay on these roads includes that caused by stop signs and traffic signals.

There are essentially two ways to examine transit performance. One approach is to use operating data from the National Transit Database to derive average operating speeds and vehicle utilization. For example, passenger-mile weighted average speed decreased slightly between 1995 and 1997, from 20.4 to 20.3 miles per hour. Another approach is to use passenger survey data that identifies travel times, waiting times, and seating conditions upon boarding. For example, the basic mobility group is more dependent on transit and has a higher tolerance for delay (12.1 minutes) and unreliability (13.6 minutes) than the other two groups. People with an automobile alternative, using transit to avoid traffic congestion, have average wait times of 7.3 minutes, with 9.3 minutes in variation. Similarly, above poverty households without cars experience wait times that are a little longer than those experienced by households with cars. They also experience a similar reliability factor.

 

 
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Page last modified on November 7, 2014
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000