Aih, at 36 weeks it's so hard to tell kan, tightening at the front with pain going to the back does sound like it could be more than just Braxton-Hicks, especially if it came on suddenly while you were driving. The safest thing would be to call your doctor or midwife and describe exactly what happened, they'll be able to check you properly and put your mind at ease, whether it's the real thing starting or just your body getting ready. In the meantime, try to rest and drink plenty of water, and if the pain gets worse or you notice any other changes, don't wait lah, just go to the hospital. Sending you lots of calm thoughts, mama!