The typical parking lot is designed to carry light loads – passenger vehicles. There will be delivery trucks, garbage trucks, and maybe, buses. If your pavement has failures with cars passing over it, there are serious problems. Trucks and buses are a different matter.
There was a rule of thumb that said each axle of a fully loaded semi-truck did the damage of 2,000 cars. I bet that very few fully loaded semis enter a shopping center parking lot. Where we see the most damage is where vehicles are repeatedly in the same wheel path. Look at the damage common in front of dumpster pads and trash compactors.
While garbage trucks would appear by their size to create the greatest pavement damage; buses are the damage champs. The common, two-axle, 40-foot bus is documented to overload pavements (1 & 2).
There are three factors which combine to make buses a major pavement performance factor:
- The typical, two-axle bus is overweight by design. With passenger loads, the bus is even more overweight. The heavier the weight, the fewer load repetitions before failure.
- Buses travel a channelize route through a property with specific stops. Truck may have several options to a truck dock or garbage pad. Buses generally have an agreed, defined route. A route could have fatigue damage, rutting, and shoving. These pavement distresses are most common where buses stop and turn along the route.
- The speed which buses travel along the route can increase pavement failures. Early pavement damage will create a rougher surface. Buses will have a slight bounce over the roughness which increases the wheel’s weight on the pavement. Pavement stress is increased; thereby, increasing the pavement damage severity. More roughness by shoving or potholes will increase in size and severity.
Trucks are essential to shopping center operations. They can be accommodated by increasing the approach to pads with Portland cement concrete and placing PCC in truck courts. Buses can be accommodated by constructing a PCC roadway for the bus route; severely limiting the route; or kicking buses off the property. All three can be difficult to accomplish. Creating a PCC route will suck up a capital budget for years. Limiting or eliminating the route will have community pushback and may run afoul of accessibility guidance.
From a cost and operational view, the Zimmer opinion is trucks are necessary and can be accommodated. On the other hand, a bus route should never be established on a shopping center property.
1)AN ANALYSIS OF TRANSIT BUS AXLE WEIGHT ISSUES
American Public Transportation Association
MORR Transportation Consulting Ltd.
202-1465 Buffalo Place, Winnipeg, Manitoba, Canada R3T 1L8
2)PAVEMENT DAMAGE FROM TRANSIT BUSES AND MOTOR COACHES
Edward Fekpe, PhD PEng MASCE
Energy, Transportation, and Environment Division
Battelle Memorial Institute
505 King Avenue, Columbus, OH 43201
Photographs from: An Analysis of Transit Bus Axle Weight Issues, MORR transportation Consulting Ltd. November 2014 for American Public Transportation Association.