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According to the results, a higher percentage of heavy vehicles in the total traffic volume is

significantly associated with single-vehicle collisions in mid-blocks (OR=0.951, p=0.049).
This result may be partly due to exposure and locational effects. Moore et al.(2011) found

that heavy vehicles had a significant effect on the severity of crashes in mid-blocks but did
not have a significant effect on crashes at intersections. Another possible explanation may be

the inadequate or poor delineation of centrelines, which has been identified as a common
contributing factor (69% of sites investigated) in heavy-vehicle collisions at mid-block in

urban Australia (Austroads, 2013). A further explanation may be the increased likelihood of a

crash resulting from a truck overtaking another truck. Such manoeuvers are more likely to
occur in mid-blocks. This finding is similar to the results presented by Ma et al., (2015), who

found that the risk of crashes was higher at mid-blocks due to lane-changing by vehicles on

urban roads.

3.5 Conclusions

The safety of heavy vehicles has attracted considerable attention from government agencies
and the general public. Heavy vehicles have many unique operating characteristics, such as

poor acceleration and stopping capabilities, high rigidity, greater mass and longer length.
These characteristics partly contribute to their over-representation in traffic fatality rates,

despite the drivers' mistakes, decision errors and speeding contribute significantly to heavy-

vehicle crashes. In addition, many heavy vehicles may experience more difficulties than
average passenger cars in certain road locations due to these unique characteristics.

Since single-vehicle crashes contribute a substantial share (69%) of truck fatalities in

Australia, this study explored differences in factors contributing to single heavy-vehicle
crashes at intersections and mid-blocks in the Melbourne metropolitan area. Crashes at

intersections are more likely to be associated with turning vehicle movements prior to the

crash (turn right and turn left), crashes that occurred on freeways/highways and main roads,
and involving heavy vehicle angle and overturn crashes. On the other hand, crashes in mid-

blocks are more likely to be associated with higher posted speed limits (60km/h and higher),
higher percentages of heavy vehicles in traffic, special road facilities and roads with divided

double lines.

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