THey still need cause to search your car. Not that they won't manufacture it if they want to. But I've been pulled over for speeding, expired tags, and other minor traffic issues a few times and have never had my car searched.
So you did get pulled over. So you were in detention/arrest (insert lawyer debate here) as in you were physically stopped. At that point the cop can search your car. He probably did. He almost certainly looked in the back seat and counted the number of passengers/objects there, something he could not do as you sped by. He then examined your life in that he looked to see if you had outstanding warrants and whether your insurance/license/registration was all in order. Had he wanted to, he could remove you from the vehicle and pat you down for weapons. Speeding, being a crime, allowed him to do these things that parking tickets do not.
"Speeding, being a crime, allowed him to do these things that parking tickets do not."
That's not entirely true (excluding the pat down). The "search" you are talking about is simply plain sight/smell/etc. A cop writing a parking ticket can look through the window of your car and run the plates to see if it's stolen, lacking registration, etc. In either case they need probable cause to do an actual search of your vehicle.
Not to mention, they can stop (in most states) you even if you didnt commit a crime, like at a DUI checkpoint.
The level of what qualifies as probable cause varies by state too. For example, I've heard that the courts in MD have held that police can pull you over and search your car on the basis that the owner has a carry permit from another state (as shown in NCIC when scanning your plate).
