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APPENDIX D ANCILLARY ISSUES A number of ancillary issues affecting truck weight enforcement were Investigated. First, a field study addressed Me issue of overweight-truck weigh-scale diversion via usage of bypass routes. The applied methodology was to collect portable WIM scale data on bypass routes and compare these data with main line WIM data. Second, implications for permitted overloads, with regard to their potential to confound M.O.E. application, were studied via a literature review and highway agency surveys to examine state-of-the-art permit record systems. TRUCK SCALE DIVERSION STUDY Methodological Approach The applied study procedure was to measure truck diversion patterns on potential bypass routes (as suggested by local officials) which circumvent operational permanent weigh scales. The experimental design was twofold: first, to detect truck diversion tenden- cies by day-of-week and hour-of-day; and second, to examine the magnitude of truck over load variation as a function of main tine enforcement activity. Portable WIM scales were deployed on potential scale bypass routes during periods when permanent main fine scales were open and closed. The applied data analysis addressed day-of-week and time-of-day patterns for potential overweight violations on bypass routes. Results Ida. . ., Results are separately discussed for field studies conducted in California arid Flor Apendix D
California The selected permanent weigh scale is located in northern California on Inter- state 5, north of the Santa Nella Village interchange. The diversion route circumventing the weigh station is Indicated on the map shown (See Figure 1) on the next page. Data were collected using portable IRD WIM equipment deployed by a field data collection ten rn from Texas A&M University. Data were collected on the scale bypass route from October 2 to October 10, 1995 allowing for seven consecutive business days of observations. No weekend data were collected due the fact that main line enforcement sta- tions were closed on weekends, hence truck scale diversion ceased to be an issue during those periods. Table 1 on page 4 summarizes portable WIM data output obtained on the bypass route. The table indicates truck sample sizes, average truck weights, and average axle- weights. The proportion of overweight trucks and overweight axles are then listed by truck type. The "Average ESALs" row lists average of total truck-specific ESALs (summed over all axles). "Excess ESALs" are then computed as the excess over the legal limit for each truck type. The table concludes with average observed Excess ESALs for violators, the proportion of violators for trucks exhibiting Excess ESAI~s and Bridge Formula violations. The table contains separate data summaries for FHWA Vehicle Class trucks, defined as follows: Type 9 Five-Axle Single Trailer Trucks Type 11 Five or Less Axle Multi-Trailer Trucks A comparison between California main line and diversion route WIM data indi- cated insignificant differences in terms of observed average gross weights, including the proportion of overweight trucks. However, trucks on the bypass route exhibited higher average ESALs and Excess ESALs. It follows that a larger proportion of trucks on the diversion route was seen to exhibit higher Excess ESALs. These findings were consistent with bypass route overweight trends observed in subsequently discussed Florida data. Appendix D 2
or lo_ . . , . ~ _ . ~ I l ~` ~ r , ~BearGu· ~ , ,,_,,,,-,,,,_ :_L ~\~ N W\N Brown Ich \ \ :0'- ,~ ~ Little Pine Canyon ~ ~. ) it. me.. . em, 9'~ and I_ PA 10 199s - ._ - ~: r ~ 1 i Mao t2.00 |ThuMar2818:371996 | Scale 1:125,000 (at center) , . 2 Mile- I r 1, 2KM 1' 1. '11 ~ r ~Hi\ I - 1 1 ii (~ ~; ~ ! California Truck Bypass Route t~1 Led ~ urn_ \Am ~ ^ ~\ I 1 - ~H \~1 if_ - ' t~ 1 1 Jon in ~ ~"~ --~~-~-- Trail Airfield ~ Spry SR, Road, Hwy Ramp ~ Geographic feature State Row ~ Park orReservat~on ' Primary State Route ~ Locale 'Interstatel;Limited Access {~?Public Airport ~~------ Utility ~---~ ~- County Boundary I Railroad Population Center · Town, Small City ~I Land Figure I. Map showing California Truck Scale Bypass Route 3 Apendix D
The data analysis also addressed Excess ESAL observation patterns by time-of-day and day-of-week. Table 2 on page 5 lists Excess ESAL violations on the bypass route by day-of-week and hour-of-day. Comparison of these data with hours of operation for the Santa NelIa ma~n-line weigh scale indicated that 70 percent of the Excess ESAL violations occurred during hours of main line scale operation, thus confirming the presence of scale diversion behavior. The observed average Excess ESAL level during hours of main line scale operation was 1.55, by comparison with 2.01 Excess ESALs when the scales were closed. However, this observed level of Excess ESAL violation between periods of scale operation and closure is not significantly different. Table I . Summary of Portable WIM Data on California Diversion Route Sample Size Average Gross Weight Average Axle ~ Weight Average Axle 2 Weight Average Axle 3 Weight Average Axle 4 Weight Average Axle 5 Weight Proportion Overweight Trucks Axle ~ Proportion Overweight Axle 2 Proportion Overweight Axle 3 Proportion Overweight Axle 4 Proportion Overweight Axle 5 Proportion Overweight Average ESALs Average Excess ESALs Proportion Exceeding ESALs Bridge Formula Violation Rate 236 484 55,854 51,849 9,405 8,598 12,933 14,128 12,087 10,235 11,295 9,787 11,140 10,034 .05 .05 .09 .03 .09 .04 .04 .05 1.4 1.9 .07 .025 .05 .02 .02 1.3 1.6 .08 .004 The majority of overweight violations occurred during the early morning hours, i.e., between 3 a.m. and 8 a.m., with the highest single-hour violation occurrence between 6 a.m. and 7 a.m. Unlike the violation trend observed at the Flonda bypass, there was no clear Appendix D 4
Date Day flour 1 0/2/95 1 0/3/95 1 013195 1 0/3/95 1 013195 1 0/3/95 1 0/3J95 1 0/3/95 1 0/3/95 1 0/3/95 1 0/3/95 1 Ot3/95 1 0/3195 1 0/3/95 1 0/3/95 1 0/3/95 1 0/3/95 1 013195 1 0/3/95 1 0/3/95 1 0/4/95 1 0/4/95 1 0/4/95 1 0/5/95 1 015195 1 015195 1 0/5195 1 0/5/95 1 015195 1 0/5J95 1 0/5/95 1 OJ5/95 1 0/5/95 1 0/5/95 1 0/5195 1 0/6195 Friday 1 016/95 1 016195 1 016195 1 0/6/95 1 0/6/95 1 0/6/95 1 0/6195 1 0/10195 Tuesday 1 0/10/95 1 0/10/95 10/10/95 Monday 1 8 Tuesday 1 2 3 4 4 5 s 5 6 6 6 6 8 9 10 10 18 18 18 Wednesday 1 5 21 23 o Thursday - Excess ESALs 1.8 2.2 2.4 0.5 0.4 3.7 1.3 1.5 4.1 0.3 0.8 0.9 1.3 6.4 1.9 0.4 0.6 1.8 2.0 2.9 1.0 5.5 3.3 1.8 1 1.1 5.3 0.9 1.2 4.7 2.9 0.2 2.1 3.4 2.0 0.1 2.9 2.0 2.1 2.8 0.9 0.8 0.1 0.9 0.1 1.0 1.1 0.5 5 5 is 6 8 8 8 8 3 8 9 10 10 11 21 23 o o 6 Excess ESAL Violations on California By-pass Route Type 9 and I 1 Trucl;s Table 2. Excess ESAL Violations on California Bypass Route 5 Apendix D
majority of violations occurring during daylight hours. An analysis of Excess ESAL viola- tiorls by severity revealed no additional hour-of-day or day-of-week trends, other than being more likely to occur during hours of main line weigh scale operation. FloricIa Me selected permanent weigh scale is located in northern Florida on U.S. Route 1, approximately 1.7 miles south of the Georgia State line. The diversion route circumventing the weigh station is indicated on the map (See Figure 2) shown on the following page. Data were collected using portable IRD WIM equipment by a field team from Texas A&M University. The intended data collection plan involved concurrent data collection (using separate WIM units) over a week-long period. Unfortunately, problems with the WIM devices precluded concurrent data collection activity; so the overall data collection was extended to somewhat compensate for this problem. Data were collected on Me scale bypass route from 5 p.m., July 14, 1995 to 1 1 a.m., July 19, allowing for 5 1/2 consecutive days of observations. Five consecutive business days of data were collected on Me main line between 5:00 p.m., July g and 5:00 p.m., July 12, 1995. During this period data were gathered on 1,789 main line trucks, while the by- pass route truck volume was extremely sparse, i.e., 63 trucks. Table 2 summarizes output generated Dom WIM output and subsequent analysis. Due to the fact Mat Me vast majority of observed trucks were Type 9, tractor wad semi- trailer, the table output is restricted to Type 9 trucks. The table indicates truck sample sizes, average truck weights, and average axle-weights. The proportion of overweight trucks and overweight weight axles are then listed by truck type. The "Average ESALs" row lists average of total truck-specific ESALs (summed over all axles). "Excess ESALs" are then computed as the excess over the legal limit for each truck type. The table concludes with average observed Excess ESALs for violators, the proportion of violators for trucks exhib- iting Excess ESALs and Bridge Formula violations. Appendix D 6
Truck Bypass Route;Routel,Florida -~ Y if rat -I ~ I jar , `~: I\-' {OI-~g ~ \ . 1~913m ITwMar2617:411996 I Scale 1:62,500 (at center) i 1 Miles ! 1 ~ 2 KM ,. i Byword Bay ~~-~~~-- Trail · Totem. Small City ~ Sty SR, Road, Hwy Rumor Airfield - Major Cot State Route US Highway Utility - ' ~ Railroad · Point of interest Figure 2. Map Showing Flonda Truck Scale Bypass Route ? . ~ . t} Public Airport State Bocn~ Popudabon Center _ Lake, Ocean, large River River, Canal _ Appendix D
Table 3. Summary of Portable WIM Data on Florida Main Line and Diversion Routes Sample Size I, 161 63 Average Gross Weight 61,933 63,691 Average Axle ~ Weight 9,546 9,297 Average Axle 2 Weight 14, 080 13,690 Average Axle 3 Weight 13,785 12,723 Average Axle 4 Weight 12,062 12, 938 Average Axle 5 Weight 12,400 13,377 Proportion Overweight Trucks .15 .26 Axle ~ Proportion Overweight .09 .13 Axle 2 Proportion Overweight .~S .21 Axle 3 Proportion Overweight .17 .19 Axle 4 Proportion Overweight .09 .22 Axle 5 Proportion Overweight .14 .32 Average ESALs 2.89 ~ I.8 Average Excess ESALs 2.78 12.5 Proportion Exceeding ESALs .19 .73 Bridge Fonnula Violation Rate .045 .048 The reader may conclude, based on a close examination of the above table, that truck weights on both the main line and bypass routes seem a little heavier than expected. While the WIM devices were calibrated by the Texas A&M data collection team at the Florida site, a question does remain regarding the precision of the observed weights. We would note, however, that this problem is inconsequential for the purpose of the ensuing analysis in that the M.O.E. applicability evaluation is based on between-Iocation differ ences. Therefore, any calibration-error effect would be offset, due to the fact that the same WIM device was used at both the main line and bypass locations. Trucks traveling the bypass route were only slightly heavier on average, i.e., 63,691 pounds versus 61,933 pounds, than those on the main line. However, a statistically signifi- cant increase, i.e., 25.8 versus 15.1 percents, was observed in the proportion of gross-weight ~ This higher-than-expected range is likely due to the calibration of the TTI WIM equipment . Appendix D 8
overload violations on the diversion route. The distribution of axIe-specific bypass-route overload violations revealed that overweight violations occurred on the mailer axles. While fewer trucks were observed to violate the gross weight limit on the main line route, those trucks which violated this limit tended to do so by a greater margin; e.g., Me average violation severity being 7,739 pounds versus 4,056 pounds on the bypass route. This observed effect is likely due to the larger main line truck volume. Heaviest main line axIe-specific violations were on the lead drive axle. The most significant difference between truck samples observed on the main line and bypass routes was the high level of exhibited ESALs. Average ESALs were ~ I.8 for trucks on the bypass route, by comparison with 2.9 ESALs on the main line route. Ac- cordingly, the level of excess ESALs was higher, i.e., 12.5 versus 2.8, for trucks on the by- -pass route. Relatively few trucks were observed to violate Bridge Formula criteria on either the main line or bypass routes. While 73 of 1,661 trucks were observed to violate the Bridge Formula on the main line, only one Bridge Formula violation was observed on the bypass route. Due to this small sample, the observed difference is not statistically significant. A primary objective of the Truck Diversion study was to examine truck violation patterns by t~me-of-day and day-of-week. Table 4 on the next page lists Excess ESAL vio- lations on the bypass route by day-of-week and hour-of-day. The clear majority of the vio- lations occurred on weekdays. The majority (approximately 60 percent) of the violations was generally seen to occur during daylight hours, e.g., between 7 a.m. and 5 p.m. Ap- proximately 40 percent of the violations were observed between ~ ~ p.m. and 6 a.m. No ex- cess ESAL violations were observed between the hours of 6 p.m. and ~ ~ p.m. The heaviest violations were generally seen to occur during the early morning hours, e.g., 6 a.m. to 9 a.m. .9 Apendix D
Date Day Hour Excess ESALs 7/14/95 Friday 17 8.8 7/14/95 Friday 21 1.3 7/14/95 Friday 22 2.4 7/15/95 Saturday 1 15.2 7/15/95 Saturday 5 0.5 7115195 Saturday 7 2.7 7~15/95 Saturday 9 24.2 7/15195 Saturday 22 0.2 7/16195 Sunday 23 16.4 7/17/95 Monday 1 23.9 7/17/95 Monday ~15.2 7/17/95 Monday ~ 2 15.3 7/17/95 Monday 15 ~7.4 7/17/95 Monday 15 4.3 7/17/95 Monday 16 16.9 7/17195 Monday 17 13.4 7/17/95 Monday 17 9.1 7/17/95 Monday 17 14.6 7/17/95 Monday 23 12.5 7/18/95 Tuesday 3 16.1 7/18/95 Tuesday 3 2.7 7118195 Tuesday 6 17.2 7/1 8195 Tuesday 7 18.9 7/1 B/95 Tuesday 9 17.6 7/1 B/95 Tuesday 13 B.9 7/~/95 Tuesday 16 2.4 7/~/95 Tuesday 16 14.1 7/~/95 Tuesday 16 6.4 7/18/95 Tuesday 17 6.5 7/18195 Tuesday 17 9.2 7/18/95 Tuesday 21 4.0 7/1 B/95 Tuesday 23 0.5 7~19/95 Wednesday ~6.7 7/19/95 Wednesday 3 22.8 7/19/95 Wednesday 4 15.4 7/19/95 Wednesday 6 21.4 7/19/95 Wednesday 7 18.6 7/19/95 Wednesday 7 17.7 7/19195 Wednesday 7 23.1 7/19195 Wednesday 7 26.4 7/19/95 Wednesday 11 5.3 7/19/95 Wednesday 11 6.4 Excess ESAL Violations on Florida By-pass Route Table 4. Excess ESAL Violations on Flonda Truck Scale Bypass Route Appendix D 10
Truck Diversion Study Summary This study examined ~uck-weight and travel trends on potential bypass routes that circumvented permanent weigh scales. WIM data were collected on both the main line and truck bypass routes in California and Florida. Similar truck overweight trends were ob- sewed in both states. Customary truck weight distnbutions, determined by average gross and axle weights, did not statistically differ between bypass and main line routes. However, trucks samples observed to use bypass routes were consistently more likely to exhibit higher average ESALs and Excess ESALs. Similar travel time trends were observed be- tween the two states; despite differing hours of main-line permanent scale operation. In Florida, in the presence of 24-hour and 7-day per week scale operation, the majority of overweight diversion activity occurred during the early morning hours, e.g., 6 a.m. to 9 a.m. In California, while t~me-of-day diversion travel was affected by permanent scale operation, a tendency was observed for early morning scale diversion, e.g., 3 a.m. to ~ a.m. IMPLICATIONS FOR PERMIT-ISSUED OVERWEIGHT TRUCKS The obviously inherent confounding factor in a WIM-based truck-weight- enforcement surveillance procedure is the absence of an accounting for permitted over- weight trucks. The general practice with regard to permitted overloads is to issue permits for the transport of nondivisible loads that exceed allowable weight limits. Single-trip permits cover either a one-way or round trip and may be valid for periods of two to 30 days. Some states issue multiple-trip permits covering periods of a few weeks up to three years. The permit issuance process ensures that routes used for these movements can ac- commodate them. Additionally, in some instances, states exercise grandfather legislative authority to issue divisible load permits for Interstate highway operation. This conces- sion accommodates industry deemed critical to the state's economy, such as agriculture arid forestry activity. This problem was investigated from two perspectives during the course of the cur- rent project. First, interviews were conducted with a number of state highway agencies to investigate the feasibility of integrating state-of-the-art automated Overweight Vehicle 11 Apendix D
Permit Record System data into an automated truck weight records database to correct for the presence of permitted vehicles. The second step, a literature review attempt to inves- tigate possible weight-distribution effects of permitted vehicles, was initiated as the result of state agency interview findings. State Highway Agency Permits Record Systems Truck overweight permit record-keeping practices were addressed with state highway agency officials in Ohio and Texas, in addition to officials of participating field study states. With a single exception, record-keeping systems for interviewed states did not provide adequate specificity to allow matching of permit-issuance data with WIM re- cords. The Texas Department of Transportation (TxDOT) operates a sophisticated, automated permitted load record-keeping system. Permit applicants call a toll-free num- ber to operators equipped with highway network mapping workstations. The operator maps out the authorized route and travel dates that are automatically input to the auto- mated record system. Thus, the permitted truck's authorized load and route are comput- erized prior to initiation of the trip. With the TxDOT system, virtually every permitted load is tracked over 77,000 miles of automated routing with sufficient precision to determine the presence of over- weight vehicles on specific routes within a 24- to 48-hour time window depending upon the length of trip. That is, truckers complete travel within a 24-hour time window for short trips. For trips across the state' a 3-day operation period is allowed; however, given the length of this trip, a trucker's presence can be estimated within a 48-hour time win- dow. Automated truck route and weight data are uploaded to enforcement agency com- puters on a daily basis. Appendix D 12
During the course of this project, the Principal Investigator met with the Director of the TxDOT Central Permits Officer confirming the TxDOT system's applicability in the evaluation of truck weight enforcement activities. Although the TxDOT system is unique, Mr. Lur~dell did offer to supply interested state agencies with the TxDOT soft- ware in order to allow their tracking of permitted overweight vehicles. Possible WIM Data Confounding Due to Permit-Issued Overloads A literature survey was attempted to gather insight regarding the possible weight- data confounding effect associated with permitted overweight truck presence in a traffic stream. A number of relevant literature items were cited. Two mathematical modeling efforts were cited which predicted truck weight distributions as a function of a variety of influencing factors (Fekpe and Clayton, 1995; and Clayton and Thom, 19911. These re- search projects confirmed the obvious. Permitted overloads do confound truck weight distributions by violating weight limit applied compliance constraints in the modeling processes. However, a field study (Middleton et al., 1988), addressing overload permit issu- ance versus actual traffic stream observation did provide significant insight regarding the extent of this confounding effect. The study compared traffic flow observations with permit oversize/overweight records. Table 5 on the next page indicates that actual per- m~tted loads in the traffic stream did not account for a sign~ficar~t proportion (between 42 and 57 percent) of illegal truck operations. The direct inference of this finding is that- field observation techniques, in the absence of permitted overload records, provide a valid indication of violation occurrence. 2 Mr. Bert Ludell, Director, Central Permits Office, Texas Department of Transportation, 125 E. ~ Ith Street, Austin, TX 78701-2483; Phone 5 12-465-3570 13 Apendix D
Table 5. Observed Truck Types Which Warrant Permits Date: 6/29/88 Date: 6/30/88 pERt~lTTED OBSERVED PERMITTED OBSERVED General Form 438 19 28 11 33 Mobile Homes 3 9 ~12 Portable Buildings 3 2 1 0 Mobile Cranes 0 2 1 4 OilService Equip. 0 2 0 2 25 43 22 51 - 42 Y. ILLEGAL 57 % ILLEGAL Source Middleton, et al. ( 1988): Conclusions Regarding Permit-Issuec! Truck Presence While the presence of permitted overweight trucks in the traffic stream can not be detected by WIM systems, the distinct possibility exists for its confounding the recorded traffic stream compliance with legal weight limits. However, the literature has demon- strated that traffic observations provide a valid indication of violations in the absence of permitted truck flow data. A further consideration is that enforcement effectiveness studies, whereby "before" and "after" periods are taken in close time proximity (so as to avoid seasonal influences), may logically be void of confounding permitted vehicle influ- ences. These effects may tend to be "washed out" by the similar presence of permitted trucks in the "before" and "after" study conditions. A state-of-the-art solution does exist to integrate automated permitted overweight vehicle data into WIM databases applied to evaluate truck weight enforcement. The automated system applied by TxDOT is available to interested state agencies as the result of the TxDOT offer to share its software. However, due to the expense of associated hardware and operational costs, this solution is not currently applicable to WIM-based truck weight surveilIar~ce for enforcement purposes. Appendix D 14
REFERENCES Clayton, A. and Thom, R.G. Gross Weight Distributions as a Function of Weight Limits, Transportation Research Record 1313, Transportation Research Board, Washington, D.C. 1991 Fekpe, E.S., and Clayton, A., Prediction of Heavy-Vehicle Weight Distributions, Journal of Transportation Engineering, American Society of Civil Engineers, Volume 121 (2), New York, 1995 Middleton, D. et al., Evaluation of Oversize/Overweight Permit Policy anc! Fee Structure, Research Report ~ lO9-IF, Texas Transportation Institute, College Station, TX 1988 Apendix D
