You can join an existing account online by clicking here. Under 'Join as an individual' just select 'Join an existing account'.
After choosing to join an existing account, you will then be asked to enter the email address of the account you would like to join. Once the email address is confirmed you will be taken through the application process.
When joining an existing account the current member will be responsible for all billing matters so you will not need any payment information.
Once the application is completed you may reach out to the account owner as they will need to accept your request to join their account. Once they accept, your application will be processed by Zipcar (this may take up to 48 hours - we'll reach out to you by email when you've been approved!).