4.3 Following Distance, Smooth Driving & Bad Weather

Space is what lets a tank driver follow the surge rules. You cannot brake far in advance or keep steady, gentle pressure if the vehicle ahead leaves you no room. The AAMVA manual (8.3.1 and 8.3.2) ties these together: drive smoothly, brake far in advance of a stop, and increase your following distance.

Drive Smoothly

Because of the high center of gravity and surge, the manual says you must start, slow down, and stop very smoothly, and make smooth turns and lane changes. Smooth driving depends on seeing things early:

• Most good drivers look at least 12 to 15 seconds ahead. At lower speeds that is about one block; at highway speeds it is about a quarter mile.
• Signal early and change lanes gradually.
• Ease off the accelerator before braking so speed drops gently.

The Following Distance Rule

The general driving section gives the minimum:

At least one second for each 10 feet of vehicle length at speeds below 40 mph. At greater speeds, add 1 second for safety.

This is a minimum. The tank vehicle section tells you to increase your following distance, so plan to leave more than the table shows, and more again in poor weather or traffic.

How to measure it

1. Pick a clear landmark ahead, such as a shadow, pavement marking, or sign.
2. When the vehicle ahead passes it, count: "one thousand-and-one, one thousand-and-two..."
3. Stop when your front bumper reaches the landmark.
4. If you haven't reached your target count, drop back.

According to accident reports cited in the manual, the vehicle that trucks and buses most often run into is the one in front of them, and the most frequent cause is following too closely. A smaller vehicle ahead can probably stop faster than you can.

Matching Speed to the Road Surface

You cannot steer or brake without traction. The manual's speed reductions:

For a tank vehicle, lower traction means surge that the tires could resist on dry pavement can now slide the truck. Increase following distance even more on slick roads.

Recognizing slippery surfaces

• Shaded areas stay icy after open areas melt.
• Bridges freeze before the road does, especially near 32°F.
• Melting ice is wet ice, which is much more slippery than dry ice.
• Black ice is a thin, clear layer that makes the road look wet. Any time it is below freezing and the road looks wet, watch for black ice.
• Vehicle icing: if ice is forming on the front of the mirror, mirror support, or antenna, the road is probably starting to ice up.
• Just after rain begins, water mixes with oil left on the road and makes it very slippery until more rain washes the oil away.

Hydroplaning

Water or slush on the road can lift the tires so they have little or no traction; you may not be able to steer or brake.

• Hydroplaning can happen at speeds as low as 30 mph if there is a lot of water.
• It is more likely with low tire pressure or worn tread.
• To regain control: release the accelerator and push in the clutch so the vehicle slows and the wheels turn freely. Do not use the brakes to slow down while hydroplaning. If the drive wheels start to skid, push in the clutch.

Retarders Off on Slick Roads

Retarders (exhaust, engine, hydraulic, and electric) slow the vehicle and reduce brake wear. When on, they apply braking power to the drive wheels only whenever you let up on the accelerator. When the drive wheels have poor traction, a retarder can make them skid, so the manual says to turn the retarder off whenever the road is wet, icy, or snow covered. In a tractor-tank trailer, a drive-wheel skid can let the trailer push the tractor into a jackknife (Section 5.1).

Space Behind and Beside You

Tailgaters

The manual's advice fits tank driving well:

• Avoid quick changes. Signal early and reduce speed very gradually.
• Increase your following distance so you won't need sudden speed or direction changes, and the tailgater can get around you.
• Don't speed up. It is safer to be tailgated at a low speed.
• Avoid tricks such as flashing lights to warn the driver behind.

Sides and overhead

• Stay out of packs of traffic; keep an open lane or shoulder as an escape route where you can.
• Know your vehicle's height and watch for low clearances.

Scenario: Rain Starts on the Interstate

A driver with a partial load is running 60 mph when light rain begins.

1. Oil on the pavement makes the first minutes of rain especially slick, so reduce speed by about one-third, to about 40 mph.
2. Turn the retarder off.
3. Increase following distance well beyond the 7-second dry-road minimum for the 60-foot rig.
4. Watch for standing water; if the steering goes light, release the accelerator, push in the clutch, and don't brake.
5. Brake even earlier and more gently for exits and stops, and slow further for ramps.

Common Test Traps

• "What following distance for a 60-foot vehicle at 55 mph?" At least 7 seconds (6 for length plus 1 over 40 mph), and a tank driver should leave more.
• "How much to slow on wet roads?" About one-third.
• "Use the retarder more on icy roads to save brakes?" No, turn it off.
• "Hydroplaning? Brake gently." No, release the accelerator and push in the clutch.