CAN a smartphone make you a smart driver?

Most BlackBerry owners, for example, know they can improve their Interstate I.Q. by using the navigation function of their smartphones, and people with a Web browser on their phone can check out World Traffic Cams to see if there is congestion at the Lincoln Tunnel before heading into Manhattan.

Indeed, our love affair with cellphones is increasingly being coupled with our love affair with the automobile, spawning applications — some silly, some sublime — that drivers can download to their mobile handsets for little or no money.

On the practical side, there are programs that help with the more mundane aspects of automobile ownership. One free application for the iPhone, for example, tries to demystify repair bills. Tap in the make and model of your vehicle along with what ails it (for instance, worn brake pads and rotors) and RepairPal spits out estimated parts and labor costs ($417 to $516 in New York City). It does not include diagnostic fees and taxes, but it does offer a list of nearby repair shops with customer ratings, should you want to comparison shop.

Conversely, on the pure fun side, there’s Dynolicious. Using the same kind of technology that enables a Nintendo Wii game controller to follow your gestures, this $12.99 application uses an iPhone’s built-in accelerometer to gauge 0-to-60 times (to within 0.08 of a second) and other performance characteristics, including lateral G-forces. Like competing programs such as g-tac pro ($19.99), Dynolicious will also let you assess your vehicle’s top speed, but to get precise results you’ll need to secure the phone in a cradle.

These programs are designed to be used on closed road courses, of course, but for those who can’t resist the temptation to test posted speed limits on public roadways, there are programs like the Njection speed trap alert application for the iPhone. The program, which costs $2.99, compiles reports from other drivers to pinpoint speed traps along your route, but the information is only as good as what your fellow speeders provide.

For those looking to decrease rather than increase their carbon footprint, there are several car-related applications that can help. Ecorio is a free program written for Google Android-based smartphones, the first of which is the G1 from T-Mobile. The application will trace your travels and, depending on your mode of transport (Hummer or subway?), keep a running tally of your carbon footprint. By tapping into Google Transit, the program can also suggest the most efficient commuting routes (less time in traffic translates into fewer carbon emissions) and in some locales like San Francisco it offers carpooling information.

For iPhone owners, another eco-friendly but less ambitious program is greenMeter ($5.99). It can estimate the number of barrels of oil your car is consuming and produce graphs illustrating fuel economy at different speeds and rates of acceleration. (As you might expect, a lighter foot will produce better fuel efficiency.) For 99 cents there’s also AccuFuel for iPhone hypermilers who mainly just want to track fuel efficiency.

Keeping up with maintenance can also help extend efficiency — and the life of your vehicle. Gas Cubby ($4.99 for the iPhone) is a maintenance and mileage program that offers service reminders and can store vehicle records that can be exported to Excel spreadsheets. Identically priced Car Care also lets you track oil changes and service expenses.

Trying to track business expenses? Trip Cubby ($9.99) and MileBug ($3.99) help iPhone owners log miles, tolls and parking for expense reports and tax purposes. You can even e-mail reports to the boss from the phone. BlackBerry users can try MileageTracker Pro. An annual subscription costs $29.90.

There’s also hand-held help for those of us who are bedeviled by senior moments, especially when it comes to parking the car. Much like a feature now available on many portable navigation devices, there are free programs like ParkMark for G1 owners that remember where you parked. Press a button to note the precise location of your car using the device’s GPS, then later, using Google Maps it will lead you back to the appropriate spot.

And for those who are reminded of the looking-for-a-bathroom Seinfeld episode, the answer is, yes. There’s a smartphone application for that, too. SitOrSquat is a free program for iPhones and BlackBerrys that locates public restrooms. It even includes user reviews and connects to Google Maps to offer directions.

If you still have trouble finding your wheels, it may indicate that you’re in no shape to drive. To track how much you’ve had to drink —and how it may be affecting your judgment—there’s .08? Blood Alcohol Content Calc, a simple but free application for the G1 that estimates your blood-alcohol level based on your weight, sex and the number and types of drinks you’ve consumed. Similar programs warn in advance that they are “for entertainment purposes only,” but Mark Britton, chief executive for the legal site Avvo, emphasizes that his company’s free iPhone application isn’t a game. Called Last Call, “it’s about helping consumers not step over that line,” he said.

Last Call calculates your blood alcohol and flashes red if you exceed the legal limit. The program will then find nearby taxi services that you can dial directly. Should you still fail to heed its advice and get pulled over by the authorities, Last Call will put you in touch with a local lawyer who handles drunken-driving cases.

Finally, should you have an accident, there’s iWrecked. This $1.99 iPhone program helps you gather all the information you’ll need should the unthinkable happen, including the location, time, names and insurance information of other drivers. You can also then use your phone to take photos of the damage and the position of the cars. Assuming, that is, that after all your travails your phone is still working.