Going fast pollutes. Very topical now, with the high temperatures.
Your telephone can track your speed.
Have an app track your speed and publish/share your ‘scores’. High speeds score less and low speeds score more. In order to prevent gaming it the app gives a ping to the central server every minute to confirm that it runs properly. The gaps that appear ask for an explanation, like ‘update/backup of phone’ or ‘battery empty’. Actually, those can perhaps also be confirmed by the app based on the condition just before and after the gap. Like 1% battery life or an operating system with a lower level. Airplane mode switched on at an airport and off at another after so many hours makes it easy to calculate the speed in between.
Those who do most commutes by bicycle and take the train to travel will score good. But driving on the highway and taking flights will score bad.
This might also favour slow trains against those high speed trains, which also pollute more.
Any takers? There is probably some government grant or a donation from a climate action fund available to fund the development of it.
Prisoners and unemployed poor people can win big time in this game. The ultra rich are the absolute losers with their private jets and fast cars. Perhaps there should be an extra metric for how much you travelled. Those who travelled at 20km/h for most of the day, like those travelling the world by bicycle, will then be ranking high.