Vehicle inspection and maintenance

A well-maintained vehicle is a basic safety control. Brakes that work, tires with good tread and the right pressure, clear glass, working lights and secure loads all make collisions less likely and less severe. Vehicle defects contribute to only a minority of collisions directly, but they often make the difference between a near miss and a crash. This lesson covers the pre-trip inspection, the main items to check, the legal inspection requirements for commercial vehicles, maintenance programs and securing loads.

The pre-trip inspection

A pre-trip inspection, sometimes called a circle check or walk-around, is a quick, systematic check of the vehicle before driving. For a car or light truck it takes only a few minutes. Walk around the vehicle in the same order every time so nothing is missed, then check the inside. Report any defect according to company procedure, and do not drive a vehicle with a defect that makes it unsafe, such as faulty brakes, a damaged tire or steering problems.

Tires

Tires are the only contact between the vehicle and the road, and their condition has a large effect on braking and handling, especially in the wet. Two checks matter most. First, inflation: check pressure with a gauge when tires are cold, and inflate to the vehicle maker's figure on the door-jamb placard, not the maximum printed on the tire. Underinflated tires overheat, wear faster, increase fuel use and can fail. Second, tread depth: deeper tread clears water and grips snow.

Most US states set a minimum tread depth of 2/32 inch (about 1.6 mm) for passenger vehicles. Federal rules for commercial motor vehicles (49 CFR 393.75) require at least 4/32 inch on steering-axle tires and 2/32 inch on other tires. Wear bars become flush with the tread at 2/32 inch, and many experts recommend replacing tires at 4/32 inch for wet-road safety and 6/32 inch for snow.

# Tread depth checks: mm and 32nds of an inch (illustrative fleet thresholds).
def to_32nds(mm):
    return mm / 25.4 * 32

readings_mm = {"LF": 6.2, "RF": 5.9, "LR": 3.1, "RR": 1.4}
for pos, mm in readings_mm.items():
    if mm < 1.6:
        status = "below legal minimum - remove from service"
    elif mm < 3.2:
        status = "replace soon (poor wet grip)"
    else:
        status = "OK"
    print(f"{pos}: {mm:.1f} mm = {to_32nds(mm):4.1f}/32 in  -> {status}")
# Pressure check against a door-placard value of 240 kPa (35 psi)
for pos, kpa in {"LF": 238, "RF": 205, "LR": 241, "RR": 236}.items():
    low = (240 - kpa) / 240
    print(f"{pos}: {kpa} kPa ({kpa * 0.145:.0f} psi) {'LOW by ' + format(low, '.0%') if low > 0.1 else 'OK'}")

LF: 6.2 mm =  7.8/32 in  -> OK
RF: 5.9 mm =  7.4/32 in  -> OK
LR: 3.1 mm =  3.9/32 in  -> replace soon (poor wet grip)
RR: 1.4 mm =  1.8/32 in  -> below legal minimum - remove from service
LF: 238 kPa (35 psi) OK
RF: 205 kPa (30 psi) LOW by 15%
LR: 241 kPa (35 psi) OK
RR: 236 kPa (34 psi) OK

Brakes, steering and lights

Signs of brake problems include a soft or spongy pedal, a pedal that sinks toward the floor, grinding or squealing, pulling to one side and a brake warning light. Steering problems include excessive play, vibration and pulling. Any of these is a reason to stop using the vehicle until it is repaired. Lights are easy to check and often neglected: walk around with the lights on, or use a reflection in a window at night. A burnt-out brake light means drivers behind you get no warning when you slow down.

Commercial vehicle inspection rules

For commercial motor vehicles, FMCSA rules require drivers to be satisfied that the vehicle is in safe operating condition before driving it (49 CFR 396.13) and to prepare a driver vehicle inspection report (DVIR) at the end of each day's work covering brakes, steering, lights, tires, horn, wipers, mirrors, coupling devices, wheels and emergency equipment (49 CFR 396.11). Since 2014, property-carrying drivers need to prepare a DVIR only when a defect or deficiency is found or reported. Defects affecting safe operation must be repaired, and the repair certified, before the vehicle is driven again. Commercial motor vehicles must also pass a periodic inspection at least once every 12 months (49 CFR 396.17).

Roadside inspections by state officers follow the Commercial Vehicle Safety Alliance (CVSA) out-of-service criteria used across North America. A vehicle found with an out-of-service defect is taken off the road until repaired, and violations feed into the carrier's Compliance, Safety, Accountability (CSA) scores, which lesson 11 covers.

Maintenance programs

Daily checks catch obvious problems, but they do not replace scheduled maintenance. A fleet maintenance program sets service intervals for each vehicle, based on the manufacturer's schedule, distance and engine hours, and the type of use. It tracks defects reported by drivers through to repair, handles manufacturer safety recalls promptly, and keeps records. Good programs make reporting defects easy and quick, so drivers are not tempted to ignore them, and give someone clear authority to take a vehicle out of service.

Securing loads

Unsecured loads cause collisions in two ways. Items falling from vehicles strike other road users or cause them to swerve, and items moving inside the vehicle can strike the driver in a sudden stop or crash. In a frontal collision at 50 km/h, a loose 10 kg toolbox can hit with a force equivalent to hundreds of kilograms. Tools and equipment in vans should be stored in fixed racks or bins, behind a bulkhead separating the cargo area from the cab, and ladders and materials on roof racks should be tied down with rated straps.

# Why loose objects are dangerous in a crash: effective force during a sudden stop.
g = 9.81
def effective_weight_kg(mass_kg, kmh, stop_distance_m):
    v = kmh / 3.6
    decel = v ** 2 / (2 * stop_distance_m)      # average deceleration in m/s^2
    return mass_kg * decel / g                  # equivalent static load in kg

for item, mass in [("phone", 0.2), ("laptop", 2), ("toolbox", 10)]:
    for kmh in (50,):
        w = effective_weight_kg(mass, kmh, 0.6)   # cab crushes/stops over about 0.6 m
        print(f"{item:8s} {mass:5.1f} kg at {kmh} km/h ({kmh / 1.609:.0f} mph): acts like about {w:6.0f} kg ({w * 2.205:6.0f} lb)")

phone      0.2 kg at 50 km/h (31 mph): acts like about      3 kg (     7 lb)
laptop     2.0 kg at 50 km/h (31 mph): acts like about     33 kg (    72 lb)
toolbox   10.0 kg at 50 km/h (31 mph): acts like about    164 kg (   361 lb)

Commercial motor vehicles must follow the FMCSA cargo securement rules (49 CFR 393.100 to 393.136), which set requirements for tiedowns, working load limits and specific commodities. Many states also have general unsecured-load laws for any vehicle, with higher penalties when debris causes injury.

Electric and hybrid vehicles

Many fleets are adding electric vans and pickups. Their daily checks are similar, with a few differences. Check the charge level and planned range before leaving, especially in cold weather, which can reduce range substantially. Inspect charging cables and connectors for damage, and never use a damaged cable. Electric vehicles are heavy because of their batteries, which affects tire wear and braking, so tire checks matter even more. They are also very quiet at low speed, so drivers should take extra care around pedestrians in parking lots and yards. High-voltage systems should be serviced only by trained technicians, and any damage to the battery area after a collision should be reported.

Using the inspection to start a conversation

A pre-trip inspection is also a moment to check the driver. Are you rested, fit and focused today? Do you know the route and the weather? Is anything on your mind that might distract you? Some fleets build these questions into the daily inspection app, so drivers confirm their own readiness along with the vehicle's. A driver who answers honestly that they slept badly can be given a shorter route or a co-driver, which is a far better outcome than discovering the problem after a collision.

Weekly and monthly checks

Some items need checking less often than daily, such as fluid levels under the hood, the spare tire, the fire extinguisher's gauge and inspection tag, and the contents of the first aid and winter kits. A simple weekly checklist helps, and the results can be recorded in the same app as daily checks.