Ten-Minute Training Topics

Vehicle Clearances

Statistics

Collisions with fixed objects are the second most common type of vehicle crashes. Hitting a guardrail, abutment or other stationary object has led to more than 11,000 deaths and more than 500,000 injuries during the most recent year’s statistics per the National Safety Council.

Introduction

When operating any motorized vehicle, we need to pay careful attention to the clearance space around the vehicle. This includes all dimensions – above, below and beside the vehicle. It’s possible to hit tree limbs, bridges, tunnel entrances, sideswipe parked vehicles and even to get stuck on railroad tracks depending on our vehicle’s design and conditions. Key contributors to these crashes include: driving while distracted (failing to notice the hazard because of electronic distractions, fatigue/drowsiness, or other impairment such as being ill or influenced by OTC medications, etc.) and/or assuming there’s adequate clearance when there really isn’t (being unfamiliar with the equipment, route, or specific hazard).

Too Tall?

If our vehicle is too tall to fit under a bridge or go through a tunnel, we could have a collision. This is especially true along the shoulders where curved tunnel entrances or overpasses may be closer to the ground than in the middle of the main roadway lane(s). This is especially common in the Northeastern part of the USA and in older cities where large roads were not designed for modern commercial vehicles.

The Federal Highway Administration specifies how much clearance is needed and how signs are provided warning of overhead obstructions. A “cushion” is supposed to be included in case the road is repaved and asphalt raises the road surface, but the local engineering team should be verifying that clearances remain adequate.

Some drivers get into trouble when they rely on GPS navigation systems that are out of date, are missing critical data, or have bad data on board. Some systems are designed for personal (i.e. car uses) and don’t have the needed insights to warn of low bridges, etc.

In addition to low bridges, we need to be alert for low hanging (sagging) wires or even overhead pipes (think about roads running through or near chemical plants, etc.). Standards call for these obstructions to have minimum clearances, too. Unfortunately, they can sag or become lower as road surfaces get taller from multiple re-paving efforts. As a driver, you have the final responsibility to exercise caution and avoid a collision.

Too Low?

If our vehicle rides low to the ground, steep humps, dips or speed bumps and curbs can create problems.

Similarly, low ground clearance may be an issue in flooding situations, or dealing with unimproved access roads for construction sites or rural roads (i.e. logging roads, park access or farm/ranch access roads).

Perhaps the most common problem is found with long, low trailers that must cross railroad tracks. In order to provide adequate drainage, railroad tracks are often built up on gravel and ballast. This provides a pronounced “hump” where the road meets the tracks. Often, this is marked with reminder signs, especially where there have been collisions in the past. The low slung trailers that can get stuck on the tracks present a hazard in several ways – a train may arrive and crash into the trailer, or the trailer may become unstable causing the load to shift. It is possible for a trailer or vehicle with long wheelbase to become stuck where the road dips as well (in a “U” shaped profile).

Too Wide?

If our vehicle (or cargo) is extra wide, we may encounter trouble when turning, passing other vehicles or transiting areas where brush and trees grow close to the road. Fortunately, there are standards to maintain clear zones behind curb lines of at least eighteen inches and as much as forty-six feet for high speed roads protected by barriers. Clear zones help in several ways – if a load overhangs, there’s some wiggle room, and if a vehicle departs the roadway, there’s some clearance area before the vehicle would likely encounter utility poles, trees and sign posts (giving the driver a chance to recover and get back onto the proper roadway.)

Additionally, specialized loads or equipment typically require a special route plan that is scouted prior to the actual trip to document clearances and ensure safety. Dealing with these specialized loads is beyond the scope of this initial report.

Another area of concern affecting sideswipes is backing up using mirrors that are adjusted improperly or may be convex (distorting the image). Backing with mirrors can lead to assumptions that side clearances are adequate when in reality your vehicle is closer than you realize. Make time to get out and look to avoid a collision.

Road & Sign Design

Fortunately, there are many standards and regulations affecting road design and signage: roads are usually engineered to provide standard minimum clearances (including shoulder widths), and signs should be provided whenever there are exceptions to these minimums.

In some parts of the country, there are “cars only” parkways which feature clearances too small for commercial vehicles. Periodically, larger vehicles find themselves on these parkways as a consequence of poor directions, over reliance on GPS systems or failing to notice a warning sign. If you do accidentally end up on a “cars only” parkway, pull over as soon as possible and turn on your hazard lights – then call 9-1-1 for assistance. Drivers who kept driving (possibly assuming they’d find an off ramp) often encountered a low overpass before they could exit the road way. If you see a low clearance situation, get out and look or find an alternative route.

Unfortunately, signs can go missing, maps may not get updated and we can encounter situations where conditions were recently changed (i.e. a road may be repaved by adding a layer of asphalt without considering that the clearances have been altered by as much as six inches, etc.) Regardless, it’s the driver’s responsibility to operate their vehicle in a safe manner by judging available (actual) clearances carefully.

Summary

As a driver, it’s your responsibility to check your route for possible clearance issues. Eliminate distractions while driving so that you can pay full attention to the road ahead for tight clearances. Always wear your seat belt to help protect you in case of a collision.

Check Clearances!

· Know your equipment’s clearances on all sides

· Plan your route with care and the proper tools/data

· Whenever in doubt, get out and look – don’t guess

· Conditions may change over time – what had been safe may be impassable now

· Driving safely is your responsibility – eliminate distractions and focus on the road ahead