A VirtualHost would also work for this and may work better for you as you can host several projects without the need for subdirectories. Here's how you do it:
httpd.conf (or extra\httpd-vhosts.conf relative to httpd.conf. Trailing slashes "\" might cause it not to work):
NameVirtualHost *:80
# ...
<VirtualHost *:80>
DocumentRoot C:\projects\transitCalculator\trunk\
ServerName transitcalculator.localhost
<Directory C:\projects\transitCalculator\trunk\>
Order allow,deny
Allow from all
</Directory>
</VirtualHost>
HOSTS file (c:\windows\system32\drivers\etc\hosts usually):
# localhost entries
127.0.0.1 localhost transitcalculator.localhost
Now restart XAMPP and you should be able to access http://transitcalculator.localhost/ and it will map straight to that directory.
This can be helpful if you're trying to replicate a production environment where you're developing a site that will sit on the root of a domain name. You can, for example, point to files with absolute paths that will carry over to the server:
<img src="/images/logo.png" alt="My Logo" />
whereas in an environment using aliases or subdirectories, you'd need keep track of exactly where the "images" directory was relative to the current file.