Evaluation of the Freeway Service Patrol (FSP) in Los Angeles

ABSTRACT

The estimated benefit/cost ratios based on delay and fuel savings for a range of typical reductions in incident durations, indicate that FSP produces significant benefits at the test site. For reduction in duration due to FSP in the order of 15 minutes, the B/C ratio is greater than 5:1. Additional benefits include reductions in air pollutant emissions, secondary accidents, CHP time used on non-enforcement activities, as well as increased safety to assisted motorist, and more efficient operation of the freeway system.

EXECUTIVE SUMMARY

Freeway Service Patrol (FSP) is an incident management measure designed to assist disabled vehicles along congested freeway segments and relieve peak period non-recurrent congestion through quick detection, verification and removal of freeway incidents. The program is jointly administered by the California Department of Transportation (Caltrans), the California Highway Patrol (CHP) and the local Metropolitan Planning Organizations (MPOs), and has been implemented on many freeway sites (beats) across the state. This report presents the findings of a comprehensive evaluation of the FSP program on a specific freeway section in Los Angeles.

The Los Angeles County Metro FSP is a partnership program jointly implemented by Caltrans, the Los Angeles County Metropolitan Transportation Authority (MTA), CHP and 20 private towing contractors. As of 1997, the Los Angeles program was comprised of 149 tow trucks patrolling 43 beats covering more than 400 freeway centerline miles in Los Angeles County. Historically there have been approximately 1,000 assists per day performed by FSP tow truck operators. The continuously patrolling tow trucks provide complimentary services such as: changing a flat tire, refilling a radiator, providing one gallon of gasoline, and removing stalled vehicles from the freeway when they cannot be restarted.

A test site was selected for the FSP evaluation based on geometric characteristics, number of in-lane FSP assists, average daily traffic, congestion levels, and the density of functional loop detectors using both historical data and new data collected by the study team. The site selected was FSP Beat 8, which is located on Interstate Route 10, between Eastern Avenue and Santa Anita Avenue.

Field data on average travel speeds and incident characteristics were collected using seven specially instrumented probe vehicles traveling at an average of 5.7 minute headways, six hours per day, for 32 days. In addition, freeway loop detector data was collected for the same time periods. Subsequent to data collection, a detailed, comprehensive, computerized database was developed. This database completely describes the traffic conditions along Beat 8 for the 32 weekdays. The database includes detailed descriptions of 1,560 observed incidents, probe vehicle travel time traces for 3,619 runs, and 192 hours of loop detector data (30-second flow and occupancy) from 240 loop detectors.

Findings

An average of 41 incidents/day was observed during the peak periods in the study area (excluding CHP-related events). The estimated incident rate was about 93 incidents per million vehicle miles of travel, and there were about 0.4 incidents per freeway mile per hour. Accidents accounted for 6.5% of all the incidents and approximately 10% of all incidents were blocking travel lanes. The average duration of all incidents was 20 minutes. Incident type, severity and the type of assistance provided were the major factors affecting incident duration. Assisted incidents lasted 24 minutes on the average, and non-assisted incidents 14 minutes.

FSP assisted 1,035 incidents during the field study (1.44 assists/truck-hr), mostly vehicles with mechanical or electrical problems, flat tires and those that had run out of gas. About 21 percent of the assists were for accidents. The average response time of FSP tow trucks was 10.8 minutes. Analysis of the CHP/CAD data and field observations of incidents by other agencies indicate that the incident response times (and durations) without FSP are longer by about 7 to 20 minutes on average.

The estimation of incident specific delay, fuel consumption and emissions for assessing the FSP effectiveness was based on the difference in average travel speeds under normal and incident conditions using probe vehicle speeds and volume data from the loop detectors. Next, the average delay savings per incident were determined by modeling each incident with different durations values. The estimated reduction in average incident delay and fuel savings for a range of typical reductions in incident durations indicate that FSP produces significant benefits. The estimated benefit/cost ratio indicates that the FSP is cost effective. For reduction in duration due to FSP in the order of 15 minutes, the benefit/cost ration of greater than 5:1. In addition, daily reductions in air pollutant emissions include a total of 60 kg of hydrocarbons, 462 kg of carbon monoxide and 122 kg of oxides of nitrogen.

Additional benefits of FSP that were not included in the calculation of the benefit/cost ratio include time and direct cost savings for the assisted motorists. Also, the FSP service results in fewer incidents attended, and reduction in the time spent on vehicle breakdowns by CHP officers, and serves as an incident detection and verification mechanism. Motorist feedback from surveys indicate that the FSP service receives excellent ratings. Furthermore, the presence of FSP provides a sense of security on the freeway, and the quicker removal of incidents could reduce secondary accidents.

Recommendations

The results of this study confirm that FSP is a successful, cost-effective operational program. Efforts should be directed to optimally deploying the FSP service on existing or new freeway beats. This requires developing a simple yet robust evaluation procedure to estimate the benefits along an existing or proposed beat based on data commonly available to partner agencies. Also, it is important to deploy the optimal number of required FSP trucks to obtain the maximum net benefit from the service.