If you're one of the record number of vacationers expected to hit the road this season, make sure the road doesn't hit back. After the human error, bad road conditions are the leading cause of auto accidents, according to The Road Information Program (TRIP).

In fact, in 1976, the most recent year for which a tally is complete, poor road conditions caused 3.6 million accidents, amounting to $5.1 billion in losses, says the non-profit research and information agency based in Washington. And, says TRIP, things may get even worse this year.

More than half the nation's 1.8 million miles of paved roads have problems that can effect safe driving, according to TRIP. This figure including narrow lanes, deficient bridges and inadequate shoulders, as well as broken and rutted pavement. In addition, thousands of potholes still linger to give motorists jarring reminders of the past severe winter.

And those roads, aside from being dangerous, also are hitting this summer's drivers in the pocketbook. TRIP notes that driving over bad roads costs 48 percent more than over good roads. Frequent slowing and stopping to avoid potholes and broken pavement wastes gas, and driving over rough surfaces increases tire wear and causes steering and suspension system damage.

To make this summer's driving as safe and economical as possible, TRIP offers this advice Stick to newer roads, such as interstates, and maintain a constant speed of 55 mph or less. The wide lanes and shoulders of interstates were built with safety and heavy traffic in mind, and their generally good surfaces can cut your driving costs by about half. Also, the accident fatality rate for interstates is less than one tenth of that for other roads, TRIP says.

"Even though the same drivers use well-designed, modern highways as well as the older roads, consistently lower fatality rates result on the better roads," said H.L. Anderson, associate administrator for safety of the Federal Highway Administration. "The only difference is that one facility is designed to accommodate many of the driver weaknesses," Anderson says.

Reducing the speed limit to 53 mph has not only saved motorists about a fourth of their gas dollars due to better mileage, it also has reduced the interstate fatality rate by about a third. And driving at a constant speed, which modern roads allow, can improve gas mileage by about a third compared with variable speed, stop-and-go driving on urban roads, TRIP says.

If you're headed for the beach or mountain campground remember that approach roads are likely to be narrow and crowded during the summer and especially on weekends. Many of these roads have soft shoulders or none at all, TRIP warns, and can be a hazard in an emergency that requires getting off the road. Be especially watchful for shoulder drop-offs when driving a recreational vehicle or pulling a trailer that may be too wide for narrow lanes on some rural and mountain roads.

Remember too, TRIP cautions, that there are 105,500 "deficient" bridges in the nation, and most of them are in rural areas.