The speed radar squeals, clocking a gray Kia Optima going 90 mph in a 70 mph zone just south of Exit 36 on Interstate 5 northbound during Tuesday’s rush hour.The driver doesn’t notice Trooper Alexis Tonissen in the neighboring lane. She drives an unmarked white Chevrolet Impala with tinted windows, its lights hidden in the grille and inside the windshield.Even if you could tell it was a cop car, aggressive or speeding motorists often aren’t paying enough attention to notice, she says.After pulling over the Optima, the 62-year-old driver says he’s just trying to get home to Tacoma. It’s a common excuse that Washington State Patrol troopers hear when they catch speeders.They didn’t realize they were going so fast. They were just going with the flow of traffic.Many motorists on this stretch of I-5 near Kelso, Tonissen explains, are just passing through. She cites the man for going 10 mph over the speed limit, instead of 20, which would be considered aggressive driving. People don’t intend for their car to be a weapon, Tonissen says, but when they drive aggressively, the car becomes one.