If your summer vacation plans involve airports instead of a road trip, you'll need to rent a car. Watch out! Rates are at historic highs because tight credit has led to smaller rental company fleets and fewer available cars. Worse, rental car companies are notorious for their costly, surprise add-on fees. So you'll want to save on a rental car by exploiting every possible discount. Here are six ways:

 1. Join a car rental loyalty club. A membership club like Hertz # 1 Gold or National's Emerald Club can get you price discounts and free rental days. You may get additional discounts if one of your credit cards has a partnership with the car rental company.

 For an upcoming trip to Indianapolis in late August to visit family, even the best discount rate I could find for Hertz from travel sites couldn't match the $33 day rate for a mid-size sedan I got by combining my #1 Club membership with a price cut from my American Express card. Plus, I'd get the #1 Club expedited check-in and avoid long lines at the airport rental counter

 2. Use travel sites to compare deals from competing car rental companies. Your best bets: Orbitz, Travelocity and Expedia. Expedia found me a  cheaper deal for my Indianapolis weekend than that $33 Hertz rate - $25 a day with Thrifty.  But I might have bagged an even cheaper rate if I had combined air fare, hotel and car rental in one package-the specialty of these travel sites.

 3. Try a car rental specialty site. Unlike the broad travel sites, carrentals.com searches just for deals on wheels. In my case, it found the same price as  the comprehensive sites. In this case it picked up the same  Thrifty  mid-size sedan like a Ford Fusion (pictured here) for $25 a day-about $8 a day lower than the Hertz rate.It also showed the same rate from Dollar. Both have offices at the airport. In some other tests, however, carrentals.com picked up rates the broad travel sites did not have.

 4. Check your auto insurance and credit card policies. They may provide automatic rental car insurance coverage, allowing you to decline the rental car company's insurance when you're arranging to get a car online or at the airport. If you belong to AAA, you can reject the rental car company's roadside assistance, since the auto group covers you for that.

 5. Avoid paying a premium for a car you don't need. If I drop my habitual midsize car for a compact like a Ford Focus, I can lower the daily rate to $20. And while being green is great, you pay dearly for renting a hybrid. A Nissan Altima hybrid or Toyota Camry hybrid could cost $63 a day.

  6. Consider a car sharing service. This service, from companies like Zipcar, work best if you'll only need a car for a couple of hours. With Zipcar, you join for $25 and pay a $50 annual membership fee plus an hourly rental rate. Zipcar's in 29 states, mostly in large cities and college towns. It's not in Indianapolis, but if I had been visiting Indiana University in Bloomington, I could have rented a Zipcar for two hours at $9 an hour including gas-$18 compared with my lowest rental company rate of $25  a day for a midsize plus gas (assuming I had been a Zipcar member).

 But Zipcar and car rental company competitors such as Connect by Hertz and Enterprise's WeCar are really less for travelers and more for city dwellers who just need a car occasionally for short periods.

Why Some People Should Buy Rental Car Insurance

So you are going on vacation this summer and renting a car. Before you log onto the rental car web site or pick up the loaner at the counter, you should think carefully about one of the first questions you will be asked; will you be purchasing rental car insurance?

If you have auto, home or renters insurance, the first phone call you should make is to your current insurance agent, so says industry experts. Explain that you are planning to rent a car and ask how your existing insurance covers damage to the rental car and the loss of personal property.

If your auto insurance includes collision and comprehensive coverage, then this should also cover the rental car within the limits of your current coverage.  Also, if you charge the cost of the rental car on a credit card, your credit card may include rental car loss damage waiver as a cardholder benefit.

But don't stop there assuming that because you have auto insurance with collision and comprehensive coverage, or charge your rental car on a credit card, that rental car insurance is a waste of your money. Here are three solid reasons why buying rental car insurance can be worth it.

• In many states, auto insurance policies do not pay for the rental car company's "loss of use" - which is the loss of rental fees by the company while the car is in the shop for repairs. If you want to cover this, then you need to buy the rental car insurance.
• Planning to drive the car out of the country? Before you do, check into the insurance limits required by those countries and you may find that your current insurance is lacking.  
• Another thing to consider is coverage for personal effects. When traveling with digital cameras, laptops and iPods, the chance something will get lost or stolen while traveling is higher. The costs to replace these items can really add up. If you have homeowners or renters insurance, particularly the form that includes replacement value coverage for personal property, then your current insurance should cover this. But many folks have increased their deductibles to $1000, $2500 or more to offset rising insurance costs. Only a loss in excess of the deductible will be covered by your existing insurance. Given the relatively low cost of personal effects coverage offered by rental car insurance, which averages about two bucks a day, the additional insurance is worth it.

Still not convinced? Then think about this. If you file a claim on your personal auto insurance policy for an accident you cause with a rented car (which may be more likely because you are driving an unfamiliar car in an unfamiliar location), your current auto insurance company may mark you as a higher risk driver. The result is an increase in your auto insurance premiums. It may be better to pay for rental car insurance for the few days rather than risk years of higher auto insurance premiums.

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