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.Supporting this observation, a recent study of Minnesota s FSPprogram found that 88 percent of the reported incidents examinedwere relatively minor, impeding traffic flow for a period of 27 minutesor less.Among this group, the incidents that received FSP assistancewere cleared, on average, in just four minutes.In contrast, the averageclearing time was about 12 minutes for incidents that did not receivesuch assistance.About 9 percent of the incidents reported during thestudy were more severe in nature.Of these, the average clearing timefor incidents that received FSP assistance was 35 minutes, while theaverage clearing time for those that did not was about 40 minutes.In short, the Minnesota FSP program proved useful for all incidentcategories, but the greatest benefit both in the number of incidentsserved and the reduction in the time required to clear the incidentsoccurred with minor incidents (MNDOT, 2004).In another study that focused on one beat in the L.A.County FSPprogram, the majority of reported incidents were also minor, with just6.5 percent of the incidents involving accidents.The study authors esti-mated that the L.A.County FSP program reduced incident-responseand clearing time by around 15 minutes on average (Skabardonis et al.,1998).The FSP studies of Minnesota and L.A.County suggest thatsignificant reductions in incident-related congestion can be achievedwith tow-truck assistance alone.Only a minority of incidents involve 304 Moving Los Angeles: Short-Term Policy Options for Improving Transportationsevere accidents that require participation from multiple respondersand result in longer incident duration.A study of Maryland s FSP program provides additional evi-dence of the benefits of aggressive incident-response efforts.Research-ers estimated that the Maryland program reduced the average incidentduration by 57 percent in 2000 and by 55 percent in 1999 and thatthe program reduced aggregate travel delay on the freeway system by15.6 million vehicle hours in 1997 (Ozbay et al., 2005).Long-Term Effectiveness in Reducing CongestionRating: Low.To the extent that incident-management systemssucceed in reducing nonrecurrent congestion on the freeway or arterialsystems during peak hours, travelers will observe that traffic appearsto be flowing more smoothly.Under the phenomenon of triple conver-gence, they may therefore begin to make more automotive trips duringpeak hours, thereby eroding some of the traffic improvements yieldedthrough incident management.In other words, nonrecurrent conges-tion will be reduced, while the level of recurring congestion will rise inresponse.This constrains the potential of incident-management strate-gies to achieve lasting long-term congestion relief during peak hours.Mobility, Accessibility, and Traveler ChoiceRating: Good.By reducing nonrecurring congestion, incident-management strategies enable existing roads to carry more vehicles perlane-mile per hour.This boosts net mobility among drivers.If busesuse the same facilities, such strategies may lead to improvements inmobility and traveler choice among transit users as well.SafetyRating: Very good.Traffic incidents often lead to secondary acci-dents.For one thing, passing drivers may become distracted by look-ing at the incident and crash into one another (i.e., a secondary crash).The stranded driver is also in harm s way from oncoming traffic.Whileremaining in the stalled car may be safer than standing in the openroadway, the driver s well-being is still at risk.Getting disabled vehicles Incident-Management Systems 305and their drivers off the highways as quickly as possible is thereforequite important from a safety perspective.While data indicate a fairly wide range in observed secondary-crash rates, most evidence suggests that such crashes represent a consid-erable portion of all traffic accidents.Estimates of the rate of secondarycrashes as a percent of all crashes range from 1.5 percent on L.A.free-ways (Moore, Giuliano, and Cho, 2004) to 35 percent on freeways inGary, Indiana (MNDOT, 2004), though some of this variation maybe due to a lack of consensus on the definition of a secondary crash.According to FHWA (2002), secondary crashes account for between 14and 18 percent of all crashes and have been estimated to cause 18 per-cent of all deaths on the freeways.A study of Minnesota freeways esti-mated that 15 percent of all crashes were secondary crashes (MNDOT,2004).On a 24-mile stretch of the Frank Borman Expressway in Gary,Indiana, 35 percent of all crashes occurring between 1992 and 1995were of a secondary nature (Karlaftis et al., 1998).Most analysts agree that incident-management strategies, byclearing disabled vehicles more quickly, can help reduce the incidenceof secondary crashes.While the precise effects can be difficult to quan-tify, efforts to estimate secondary-incident reduction resulting fromvarious incident-management strategies have been reported in the lit-erature.In Pennsylvania, the Traffic and Incident Management Systemwas estimated to reduce secondary crashes on highways by 40 per-cent between 1993 and 1997
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