Purple Semi is the best road trip game yet invented... by me.
The rules are pretty simple: you win points for every Purple Semi that you call ("Purple Semi!!") & someone else in the vehicle approves. A Purple Semi must be approved by someone else in the car or you actually loose the points you were about to win.
So, it'a a game for sharp eyes and a bit of strategy. If you call a Purple Semi that no one else sees, you loose points. If you call a maroon semi Purple, you loose points. (If you call a Purple Semi at dusk, be very careful as that's when all semi's start looking purple!)
To win BIG points you need to spot rare Purple Semis, that is, Purple Semis that are doing something less usual than just driving past you in the other lane.
For example, I once won Purple Semi against my husband for an entire year after I spotted a Purple Semi getting pulled over by the police. Purple Semis on overpasses or parked behind Dairy Queens (see above) are also worth more points.
How many more points is up to whoever is playing the game! So it's up to you at the beginning of the road trip to predict any unusual Purple Semis you might see & agree in advance on how many points will be assigned should such a Purple Semi be spotted. Should you spot an unusual Purple Semi that has not been pre-determined, that's your chance to get into debate mode. Argue your case to your car-mates, give reasons why your semi is so special & unusual. Everyone must agree on the score. (Start working on building allies early in the trip.)
When my girlfriend & I went up to Tacoma to see Lady Gaga, we agreed in advance that our scores would be tallied up over the whole 2 day trip & that if one of us spotted a Gaga Purple Semi we'd be awarded 10,000 points. Neither one of us did see a Gaga Purple Semi but at the end of day 1 she was up 70 points to my -20. On the return trip I did much better & managed to spot so many Purple Semis that by the time we got home I'd evened the score & won by 10 points.
Now you know! Go play!