Under Tennessee law, injuries resulting from a dangerous condition on property involve questions of reasonable care by 1) the property owner/operator, and 2) the person using the property. The law does not require property owners to prevent all injuries - only to take "reasonable" care to guard against risks of harm. The greater the knowledge of a risk, and the greater the harm, the more a property owner is held to do something about the situation. There is an equal duty on the person using the property to act reasonably - seen from the perspective of the community as a whole, not just your particular normal habits. Issues about whether the gate should have a sensor are part of the balancing of what is reasonable under the circumstances. So long as a property owner has taken some reasonable measures to take care of their property, the law is not going to require a specific measure be taken to avoid a specific harm.
This sounds like an old state bar question. Seriously, assuming you and / or grandson suffered injuries, I think you both should get medical attention. With respect to liability, I think the gate probably malfunctioned and you may have claim against the apartment complex. There might be some comparative negligence for walking through the area designed for vehicle and not pedestrian but if it is commonly used by pedestrian, then that would shift more blame to the complex, in my opinion. With respect to the transport people difficult to say because if they left you in a place of safety then they may have fulfilled there duties. Were you unable to walk to your apartment without using the driveway? or was it more convenient? If the MATA is government agency or service, then government claims would need to be filed.
You really need to contact counsel in your state to review your situation.
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Everyone you mentioned could potentially be liable. None of that will really matter much unless you or your grandson suffered some significant injury. If there were no injuries then such a claim would have little value and you will have a hard time finding a lawyer willing to pursue such a claim.
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