This is not legal advice.
Avis uses American Traffic Solutions to bill fines incurred during rentals. At least on the East Coast they do, and since ATS is in Phoenix I don't know why they wouldn't cover your ticket also. I have two email addresses for them:
[email protected], and
[email protected]
I've gotten parking tickets in the past (admittedly easier to handle than your red light ticket situation because I've had the citation number, so not perfectly analogous) and I've sent an email like this to both emails, also copied to Avis via online form:
Dear Sir/Madam:
1. By this email, I am writing to inform you that I have contested District of Columbia ticket #xxxxxx, incurred during an Avis Rental, Rental Agreement #xxxxxxx. Please do not send payment for this ticket or bill me for this ticket.
2. By this email, ... (same)
I expressly revoke any permission granted (and in doing so do not acknowledge or affirm any such grant of permission) to pay these citations on my behalf. Please contact me with any questions.
Sincerely,
[you]
They sent an auto-responder confirming receipt. When they later billed me for the tickets anyway, and I contested the charges with my credit card company, this correspondence was sufficient to win the dispute even though they answered affirmatively with my rental contract. YMMV.