IllegalVeh: % of identified problem vehicles operate illegally

There may be some fraction of vehicles operating illegally without undergoing the requisite repairs or certifications needed to pass or be waived from the I/M inspection process.

Upper: 6.6%

Lower: 13%

Motorcycles and light trucks: 20% (0% - 40%); buses and heavy trucks: 10% (0% - 20%) (Triangular distribution)

The illegal operating rates may be higher in the BMR since the I/M programs are less mature. It was assumed that for motorcycles and light trucks, the rates are both 20%, and for public transits and heavy trucks, the rates are 10% since it should be easier to identify the violations by these vehicles on road.

GoodRep: % of repair work initially effective

Some fraction of repairs are not effective but falsely pass re-tests. For example, random roadside tests show that a portion of the vehicle fleet fails I/M immediately after being repaired but then pass an official I/M test.

Upper and Lower: 80%

72%

(44% - 100%, triangular)

Available information related to this variable is very limited. A study by Land Transport Department of Thailand randomly selected 21 private inspection centers in Bangkok and requested two problem motorcycles to be tested by these inspection stations [7] . The two motorcycles were failed by 12 of the 21 stations whereas passed by the remaining 9 stations [7] . This study indicates that only 58% ( $1 - 9 \div 21$ ) of testing vehicles may properly pass the I/M. It was assumed that the updated I/M in the BMR considered here will improve the performance of this variable and achieve 90% of the US level. Therefore, the value of this variable is: $90 % \times 80 % = 72 %$ .