Hiring a car in Houston is recommended, because it is cost-effective and allows you to explore parts of the city which are not covered by the Light Rail. Having said this, driving during the rush hours(07.00 - 09.00 and 16.30 - 18.30) is not advisable as the roads tend to be congested.
Be extra vigilant whilst driving on the highways of Houston because many tend to drive recklessly. Speeding, lane changing with proper signalling and abrupt turnoffs are quite common. Always know where you're headed and which exit you have to take, before you enter the highways. It's also advisable that you carry a map with you at all times.
Check with the Texas Department of Transportation Info Hot Line (tel. 713/802-5074) for any lane closures, before you get behind the wheel.
Parking in Houston is not a major problem like in other cities, although at times it may be difficult to find any in Downtown. Most centers and venues have free parking for tourists/visitors.