I know that the national calling frequency is 146.520. Everywhere I go, it does not give a DUP or TSQ. I am not trying to be or, ask a crazy question but is there or not.
146.520 MHz is the national calling frequency for FM voice. It's a "simplex" frequency, meaning that you call on this frequency and then listen for a reply on the same frequency. (It is "national" in the US, but that does not guarantee that many people are actively monitoring this frequency! YMMV)
If you're interested in other modes, there are other more-or-less standard frequencies, like 144.200 for SSB voice.
Check http://www.arrl.org/band-plan for frequencies and sub-bands for various amateur bands and operating modes.
I have my VHF rig in my pickup truck set to 146.52 MHz all of the time when I am driving. In an hour's time I would guess I hear maybe 3 or 4 copyable signals. My main use is to help someone out by answering questions that are asked (frequently, traffic snarls and/or other travel related things of mobile operators).
Also, not long ago I was stuck in traffic (south of Tacoma, Washington on I-5) and so I raised up a question on 146.52. Another guy, traveling in the opposite direction (south-bound) had just passed the accident causing the backup that was about 2 1/2 miles north from my location. We chatted he got out of range for easy which I am guessing was about 7 to 10 miles.
It is not uncommon for ham radio operators who normally operate HF to have their VHF rig set to 146.52 whether in a vehicle or at home. In a large city, you can use the simplex 146.52 traffic to ask advice on restaurants or routes or directions and usually pick someone up. Not as predictable as a repeater but it is a lot easier than programming in your repeater tone while driving in other cities.
In some areas where there are a lot of active HAMs you might hear some traffic.
Also if you want contacts you do need to call. Just listening for some else to call is seldom a good strategy.
Keep in mind that VHF is fairly sort range especially with a low antenna mount like a car driving down the road in a valley.
if you are looking for conversations when travelling, you might have better luck finding the information on local repeater for the are you are travelling in.
To answer part of the original question that hasn't yet been answered, duplex (a.k.a. offset, meaning repeater mode) isn't used on the VHF calling frequency used in the US and Canada, 146.52 MHz. Neither is a tone squelch code, a.k.a. a "PL" tone, properly called a CTCSS tone. Just plain old FM simplex.
I would think that the calling frequency tends to be used more in rural areas than in big cities. I live in a rural area, and I hear occasional traffic on it, which is more than I can say for most of the repeaters. Someone is as likely to be monitoring the calling frequency as the major repeaters in a small town, which makes it a good resource for travelers just passing through; no need to grab the directory and guess which repeater is the one that people actually use.