Although I don't have any personal experience with it, I remember one user (possibly it was Mallikarjuna) reported good results with the Garmin Nuvi 660 GPS (which no longer seems to be available). I don't know what, if any, tricks were involved in getting that to work.
I imagine some other models from the Nuvi will also work fine, but from looking at the online specs for the current Nuvis from Garmin, I can't tell why the other user's Nuvi seemed to work fine and yours is giving some trouble. In other words, I can't tell whether the Nuvi 660 GPS is among a discontinued line that used to cooperate with other software (and the newer Nuvi 205 no longer cooperates), or whether they all cooperate and should work just fine with Tru-Traffic, but there's something else amiss in your particular case.
Since most auto GPS units that i've seen use a mini USB plug there is no way I can directly connect any of them to my laptop serial port.
If you're using Franson GPSGate software, then you shouldn't need to connect with a serial cable, as that software will emulate a serial port for Tru-Traffic to use. But I appreciate that if Franson GPSGate isn't recognizing the GPS receiver connected with a USB cable, then something else must be done.
Do the Nuvi setup menus suggest anything that could enable/disable communication with other software?
Can you get it to work with GPSBabel?
Mallikarjuna may be able to offer some suggestions from his experience.
We must make a distinction between (simple) GPS receivers and (more sophisticated) GPS navigation devices. The former tend to work fine with Tru-Traffic (and with other software), and the latter, which include the Nuvis, don't always cooperate with other software as they're designed to be self-contained for their intended purpose (navigation).
What is the simplest (quickest) setup to be able to use Tru-Traffic for travel time studies?
The simplest (quickest) setup is probably to go buy Microsoft Streets & Trips 2009 with GPS Locator (make sure it says "with GPS Locator") and just use the enclosed GPS Locator. You can buy it at Staples, Office Depot, Best By, etc. For travel time studies, you don't need to install the software Microsoft Streets & Trips 2009, but it's nice software, so you may want to install it all the same. Think of it as a bonus.
With only a little extra effort (for just the purchasing part, not for the subsequent setup/running part), I recommend the Pharos iGPS-500 Convertible GPS Receiver even more highly, as its chipset makes it a more sensitive GPS receiver than the one from Microsoft. You should be able to use either the USB or the Bluetooth configuration. I like the USB configuration, since it draws power from the laptop, which is plugged into the vehicle power outlet (cigarette lighter).
The user manual suggest the Pharos receiver as a simple option. Is this the Pharos i500 III?
Yes, I think
so. On the Pharos web site, I see mention of the "iGPS-500
Convertible GPS Receiver", but no mention of the "i500 III
", so I'm just assuming we're referring to the same thing. The Pharos GPS receiver that I and others have liked quite a bit is the iGPS-500 Convertible GPS Receiver.
Does this connect directly to the serial port or does it need a USB to serial cable?
It connects directly to the USB (not serial) port, and its driver emulates a serial port for Tru-Traffic to use. It does not need a USB to serial cable.