I'd call them less a solution, more an attempt at harm reduction.
And the only things they'll properly resolve are tailpipe emissions and idling noise. At least one of which is of no concern when dealing with the externalities of car traffic.
If you really want to solve the environmental impact of transportation, you minimise the need for transportation. Put homes and workplaces close together, offer mass alternatives for the pairs where you really do need motorised mobility solutions, and minimise the number of situations where it's more convenient to take a car. Ban on-street parking and heavily tax off-street parking. Need to park your car in the city? Hope you can afford to pay an arm and a leg. Oh, you can't? Looks the Park & Ride at the train station two towns over is the nearest alternative. Don't worry though, the trains go six times an hour and a day ticket is, like, four quid max.