The end of California highway 111 becomes Calzada Lopez Mateos just south of the Mexican Customs checkpoint. Follow the signs that will point you to San Felipe or San Luis. You will pass by a large shopping mall on the east side of the boulevard, the Centro Civico (Civic Center - Mexicali's official "downtown" area), cross an overpass, and after a few minutes you will see large signs for Wal-Mart and Sam's Club on the west side of the boulevard. The cross-street where these stores are located is Bulevar Lazaro Cardenas, a large east-west boulevard which is also the highway from Tijuana on the Pacific coast leading to Sonora and the Mexican mainland.
At Lazaro Cardenas, make a left turn, then stay near the right as you head east. After approximately 1km (.6 mile), you will see a large monument in front of you and an underpass. Do NOT take the underpass - stay right, and prepare to make a right turn to head southeast again. This will put you on Avenida Benito Juarez. Head south for another km (.5 mile), and you should see a green sign for SCT in the center of the roadway, along with two banks on the east side of the avenue (Banamex and BITAL). Make a left turn on that street that goes between the two banks, and head east.
Once on the side-street off the larger avenue, you will drive by a school playground, and look for a green overhead sign with SCT on it. At the stop sign just past that overhead sign, make a right and head south a couple of blocks to another stop sign. Then make a left turn, and the SCT complex is on the south side of the street - all the way to the next stop sign.
Here is a map showing the area around the Mexicali SCT office:
Telephone: +52 (686) 561-93-40
Web page: http://cgpc.sct.gob.mx/index.php?id=453
Jefe (Chief) of the department: Jose Luis RODRIGUEZ Cervantes (a ham, XE2CF, although he is not active - avoiding conflicts between the hobby and his job)