The border crossing at San Ysidro is open 24 hours a day. Farther east, the Otay Mesa crossing is open daily from 6 A.M. to 10 P.M. A third border crossing in Tecate, CA is open from 6 A.M. to midnight. 
Visitors to the northern part of Baja California do not need passports or tourist cards if staying in the country for 72 hours or less. If you plan to stay longer or travel beyond Ensenada, you'll need to obtain a tourist card. This document is free of charge; proof of U.S. citizenship is required. 
We also feature a updated report on the wait time for the San Ysidro, Ca. and the Otay Mesa Borders Please visit: 
http://www.planetabaja.com/garitas_html.cgi  

Ways to get there: 
Less than 20 miles south of downtown San Diego lies the world's busiest port of entry - the international border crossing between San Ysidro, CA and Tijuana, Mexico. Here are several ways to get to the border. 
By Bus: (800) 231-2222 
Greyhound Bus Lines offer daily service from San Diego to Tijuana. Costs between $5 and $9. 

By Car: 
Drive to the border, park at one of several pay parking lots on the U.S. side and walk across. Parking rates average $2 per half-hour or between $6 and $10 for 24 hours. 

By Trolley: (619) 231-8549 
The San Diego Trolley is an excellent alternative; regular service is provided from downtown San Diego. The trip takes approximately 45 minutes and the cost is $1.75. 

Mexican Auto Insurance: 
If you plan to take your car into Mexico, you must purchase Mexican automobile insurance prior to crossing the border. Most U.S. policies are not valid in Mexico. In the unfortunate event of an accident, only a Mexican insurance policy will be recognized as valid. 

Border Insurance Services: (800) 332-2118 
Mexican Insurance by phone. Representing the largest and most reliable Insurance Company in Mexico. 

Mex-Insur, Inc.: (619) 428-1121 
213 Sycamore Road, I-5 at the Via de San Ysidro exit 
San Ysidro, CA 92173