Drafting is most important at NASCAR's restrictor plate tracks, Talladega Superspeedway and Daytona International Speedway, where the plates mean that much less power is available to push the large bodies through the air. Race cars reach their highest speeds on these superspeedways, so the aerodynamic forces are highest, and the effects of drafting are strongest. Since restrictor plates were first used as a safety device, their effect has changed the nature of drafting. Vehicles no longer have sufficient horsepower or throttle response to maintain their drafting speeds upon exiting the draft; they can pull out and squeeze ahead but lack the response to clear the car being passed. This negates the slingshot maneuver. As a result, passing is often the result of cooperation between two or more drivers or is achieved by sucking air off the side of the car being passed, a technique called side-drafting.