On our recent trip to Madinah, we wanted to the test what some people call a “gravity hill’ and some people call the “work of jinns” in Wadi-e-Al Baida, alternately called Valley of the Jinns. The driver of the taxi van tested the vehicle on the stretch of road between the valley and Madinah both ways – in reverse and going forward. In both cases, the vehicle when placed in neutral; moves towards the direction of Madinah. Here is the link of a person who proves that it is the downwards slope that pulls the car towards Madinah. Here is another link that cites religious aspects related to AlBaida.
I think it is a little bit of both. Initially when the vehicle starts from the valley, it quickly accelerates and reaches speeds of 140-160 km/hr which could be attributed towards the downwards slope (which btw appears like an uphill slope or a flat road). The downhill appearing as an uphill or a flat road can perhaps be explained by the theory of optical illusion. But later on the vehicle keeps on going at a steady speed of 110 km/hr for a big stretch of the road. I would, expect, by the theory of physics that if a vehicle goes downhill, it should accelerate and not have a steady speed. I need to research that aspect further. The vehicle stops driving by itself once it reaches the Al Khulail Dam.
Anyway, here is the video – you decide!