Response to MassDOT Questions June 17, 2011
•We are interested in seeing the back-up data on how the truck crash rates were calculated
based on the limited amount of data available. Also, should the crash rates be weighted to
reflect the severity of crashes since minor incidents are unlikely to result in an explosion or
spill?
•The accident rates were estimated by UMass at the request of Lieutenant Fitzgerald of
the State Police. Battelle does not have the raw backup crash data contained in the UMass
Data Warehouse.
•Only “serious” crashes reportable from the state to the FMCSA were used so there
would be no minor crashes.
The determination of the accident rate was a collaborative process between Battelle and the
University of Massachusetts. UMass already had a GIS system of the Massachusetts roadway
system and had also identified and geocoded all the commercial vehicular accident locations (by
latitude and longitude). Battelle maintains the Freight Analysis Framework for the Federal
Highway Administration, a GIS system containing AADT (average annual daily traffic) flows
and the fraction of those vehicles that are trucks. The accident rate is obtained by dividing the
number of accidents by route segment (the UMass crash data) by an estimate of the total annual
vehicle miles traveled on the route segment (obtained from the Battelle data) both components
were available to obtain an estimate of the truck accident rate by route type. Battelle worked
closely with UMass staff to line up the route segments in the Battelle data set with the UMass
dataset. The UMass team then calculated the accident rates by route type. Battelle did not
request the raw accident data. Instead, Battelle verified that the accident definition being used by
the UMass team matched the FMCSA definition of a serious accident.
The accident rate calculation procedure was as follows:
1. Using the truck percent values for coincident roadway segments on the FAF network,
determine an estimate of truck percent for each functional classification (unique
combinations of urban type and functional class fields). Estimated average by calculated
on a mileage weighted average. Estimates were calculated as well as the percentage of
mileage for each functional classification with truck percent estimates for coincident FAF
roadway segments.
2. Apply the estimated average truck percent by functional classification to all roadways
segment in the state that did not have estimates from coincident FAF network roadway
segments.
3. Calculate the truck VMT (Vehicle Miles Traveled) for each roadway classification.
4. Tabulate the number of truck crashes by functional classification from UMass Data
Warehouse where truck crashes are defined per Federal Motor Carrier guidelines.
5. Calculate the estimated truck crash rate for each functional classification.
•How many of the truck crashes involved NRHM cargoes?
•UMass determined accident rates for urban, urbanized, and rural areas, for the
years 2007 – 2009. Based on discussions with UMass, all of the routes included
in the Battelle Hazmat Route Evaluation are in urban areas so the accident rates
for urban areas was used to estimate a truck crash rate on Massachusetts roadways
by urban type and functional class based on estimated annual truck miles
extrapolated from truck percent on coincident FHWA Freight Analysis Network
(FAF) Roadways. The truck accident rates in urban areas were based on the
following numbers of truck crashes:
•Local -1,347
•Interstate – 1,881
•Principal Arterials – 1,096
•Urban Principal Arterial – 1,893
•Urban Minor Arterial – 2,200
•Urban Collector - 847
We did not request that UMass identify the number of NRHM crashes included in the
calculation. A typical fraction might be 4 percent. Considering the 1,881 interstate
crashes, less than 100 crashes in three years would involve NRHM shipments. However,
it is not appropriate to base the accident rate calculation on NRHM-only crashes because
this increases uncertainty of the accident rate estimate. From a statistical power
viewpoint, uncertainty in the accident rate estimate increases rapidly as the number of
crashes being considered decreases. FHWA Guidelines for Applying Criteria for
Highway Routing of Hazardous Materials (1996) indicates (p. 18) that because of the
infrequent occurrence of hazardous materials accidents, information on accident rates
involving only vehicles carrying hazardous materials, along certain routes or route
segments, that results in the release of hazardous materials, are “generally not available.”
The FHWA Guidance goes on to state that “[t]herfore, it is necessary to use accident rate
data that are the best possible surrogates…accident rates for all trucks or even all vehicles
may be substituted. Generally, truck accident rates should be used, if available, as long
as the sample size is sufficiently large. At least three years of accident data are preferable
to determine accident rates.” The commercial motor vehicle accident dataset, described
above and available from UMass, met this criterion.
•There should be some explanation on what roadway functional classifications were used
along each proposed route.
•The roadway functional classifications were specified using a map on the MassDOT
website. http://services.massdot.state.ma.us/maptemplate/RoadInventory
•If as part of the formal public notice and comment process, if a revised final report from
Battelle is requested by the City and prepared, we can add the definitions MassDOT used
to assign a “roadway functional class” to the routes shown on the above website.
•The federal regulations require that exposure to "water sources such as streams and lakes;
and natural areas such as parks, wetlands, and wildlife reserves" be measured. Did Battelle
perform this analysis? If not, we request that Battelle measure this potential exposure.
•Yes, this analysis is included in the report.
•The measured burden on commerce lacks specific details about the number of trucks that
will be impacted and does not speak to the impacts from the different fleet scheduling required
with the proposed restrictions. The City should determine how many hazmat trips are made on
a daily basis. Additionally, the numbers used to measure the burden on commerce are largely
indefinite and assume a day-time only restriction. This does not appear to provide any
calculations supporting a 24-hour restriction.
• Neither Boston nor MassDOT had ever performed a detailed hazardous material
commodity flow survey in the Boston Metropolitan Area. Limited one-day truck counts
had been done in two instances by the Boston Police truck team back in 2003 and 2005
and that older data was reviewed. We obtained video tape records from Boston traffic
cameras but it was not possible using these videotapes to identify placarded trucks using
the surface streets in downtown Boston given the inherent limitations of the camera
monitoring systems. In addition, we were unable to differentiate between through trucks
and those making deliveries within the City. We attempted to estimate the number of
shipments by sending out a questionnaire to over 1,200 carriers and shippers. Using the
results from the 150 that replied, it was not possible to get a verifiable or accurate count
of the number of daily HM shipments through downtown Boston. Several truckers
stated information on the number of daily shipments was company proprietary. We also
used data from Boston’s hazmat permit application as another source for potential
hazmat shipments. In the absence of formal commodity flow survey results, we believe
that the impact on commerce can still be meaningfully estimated on a per truck
shipment. .
•The logic for using the half mile impact radius seems appropriate for route planning, but it
does not provide enough differentiation to compare the downtown Boston routes. We
recommend that the City use a smaller radius to perform a second evaluation of the city routes
to help prioritize between them.
• Calculating risk based on using a smaller impact radius to help differentiate risk among
routes is not required in the routing guidelines and, even if it were possible to undertake
such an analysis, it would require considerably more estimation work allocating
population along the routes using GIS, introducing greater uncertainty in the relative risk
exposure estimates. Furthermore as one goes to a smaller radius, such as one hundred
meters/110 yards, a larger and larger fraction of the population becomes transient, a part
of the population that is very difficult to measure and has a strong temporal distribution.
For example there are many more people in close proximity to the hazardous material
routes during rush hour periods than at midday or in the early hours of the morning. In a
sense the assumption being made is that the number of directly exposed people is
proportional to the number of individuals within ½ mile of the hazardous material route.
The people within this area are also the number of people that potentially could be
present within the most catastrophic impact area for a hazmat release and consequently
at risk for death or serious injury.
•During the public process there will undoubtedly be questions on how the City will permit
hazmat carriers. Does the City intend on maintaining a permit process for point of
origin/destination deliveries? If so, what will this process look like?
•This is a question that will have to be addressed by the City with the assistance of
Battelle.