Most highway vehicles have the advantage of being able to move two-dimensionally, unlike a train on tracks, so a directional handheld antenna is a real advantage.
I have found that with small dipole antennas mounted remotely, that so much signal is attenuated in the length of cable that the advantage of gain is almost lost, except with a real high gain design or in conjunction with an amp.
I am installing two yagis to bridge the gap between my house and my mother’s, but not being a radio amateur, much of this is trial and error.
The transmitter hunt was conducted by having all participants gather at the starting point. Odometer readings were recorded. At 5 PM the transmitter is switched on. When the participant finds the transmitter, the time is recorded and mileage is recorded. The sum of miles and minutes is your score. Low score wins. Using the DoppleScAnt, you can get to the transmitter as rapidly as driving conditions permit. Do a Google search for DoppleScAnt to see PDF drawing of the designs.
If you want to get better results on your 2.4 GHz bridge, I recommend using an Ethernet Bridge with Power Over Ethernet to put the transmitter as close to the antenna as possible. Minimize the coax losses with very short runs or select LMR400 with type-N connectors to reduce the losses. I purchase most of my 2.4 GHz "toys" from Hyperlink Technologies. If you have a small order, they have an e-Bay shop. They sell 2.4 GHz inline, pole mounted amplifiers. You'll need to make sure the amplifier is just overcoming the coax loss so your effective radiated power doesn't exceed FCC limits. The amps are available in bi-directional models. Remember than an amplifier amplifies signal and noise. You're ahead to get the Ethernet converter closer to the antenna in preference to a long coax run.
Look for a book called "WiFi Toys" at the bookstore. There are some fun projects in there.