Mr Mehra, 35, was returning from a wedding with the teen, when a speeding van overtook his Wagon R car on a flyover.
When he objected, an argument started. In the middle of it, one of the men got off the van, shot him and made off.
Mr Mehra was taken to the local police station by his nephew and his teacher, who had also attended the wedding and met them on the road. When he was finally taken to the hospital, the doctors declared him dead.
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.