Cars with light bars

2015 Audi RS 6 Avant

2016 BMW M4 GTS

2011 Bugatti Veyron Super Sport

2017 Chevrolet Camaro ZL1

1996 Chevrolet Impala Super Sport

2021 Ford Bronco

2010 Ford Crown Victoria Police Interceptor

1959 Jaguar MK II 3.8

2016 Lamborghini Aventador Superveloce

2011 Mercedes-Benz SLS AMG

2014 Mercedes-Benz Unimog U5023

2008 Mitsubishi Lancer Evolution X GSR

2014 Volkswagen Golf R

The light bar is an upgrade you can buy to some cars.
From Custom Upgrades: Go to Aero and Appearance -> Side Skirts and choose the color of the light bar you prefer.
*Note: Only the cars listed above have this upgrade.