A T-junction house is considered bad feng shui for several reasons. The main reason for the bad feng shui reputation of a T-junction house is the fact that the Universal energy (called Chi) is rushing too strongly from the road towards the house; this negatively affects the energy of the whole house.
In many cases, you can feel how the energy of the T-junction literally "hits" the house with sharp, aggressive, Sha chi quality of energy. This happens especially if the house is energetically exposed, meaning it has no landscaping around it and it is situated very close to the road.
The other variable will be a short road with light traffic, in which case the negative effects will be minimal if any at all.
In feng shui, the traffic on the road is often compared to the flow of the river. The stronger the traffic, the stronger the river flow. This is an easy way to feel or imagine the energy rushing into the house. The difference, though, is that with the river you get high-quality energy, even if it is rushed, when with cars you get stress and high pollution.
Improving the House's Feng Shui
See what you can do on the outside, as well as on the inside regarding the T-junction energy. Smart landscaping to protect your front door, as well as any windows that are "hit" by the rushing energy, is the best feng shui solution.
You can also neutralize/soften the energy from the inside. For example, you can have a row of plants on the windowsills of all windows that are facing the road. One or several crystal clusters can do a good job in the windows of a house facing the T-junction. Smart window treatment can also lessen the negative effects of the T-junction energy.
Many feng shui consultants recommend a bagua mirror on the outside of the T-junction house, see if you like this feng shui cure for your house.
A similar challenging feng shui situation is occurring with the Y-junction houses, but with a slightly less challenging feng shui. A Y-junction house can create a "missing opportunities" energy for people living in the house, thus it is important to activate and balance its energy on the outside, as well as on the inside.