Interstate Highway System
This article is a travel topic
For many trips, the interstate highways are the most efficient way to travel by automobile between two points. Being limited access highways, interstates do not have traffic lights except on rare occasions. They typically have speed limits of 55 miles per hour (89 km/h) or more - portions of I‑10 and I-20 in rural western Texas and portions of I‑15 in rural central Utah have a speed limit of 85 mph (137 km/h) - and are well maintained.
 Numbering system
The number that is assigned to an interstate highway has a specific meaning in identifying its purpose:
This order of numbering is opposite from the U. S. Route System in order to avoid overlap of identical numbers. There is currently one instance of an interstate highway and a U.S. route of identical numbering overlapping: I-74 and US-74 in North Carolina. There is also a section of US-41 in Wisconsin that is proposed to become a section or I-41.
In Hawaii, interstates are numbered with the letter H followed by a number.
 Types of signs
 Speed limits
Like most other roads, all interstate highways have speed limits. The limits, which are controlled and enforced by state and municipal police departments in the respective states where they are located, can vary, depending on the laws of that state, the volume of traffic, and other factors. Typical speed limits range from 55-75 miles per hour, though there are exceptions both above and below this.
In the past, it was widely accepted that there was a grace of 10 mph above the speed limit before tickets would be issued. This has changed in most states though, as excessive speed has been found to be the most common cause of fatal accidents. Now, in most states, tickets are routinely issued for speeding violations less than 10 mph above the speed limit, and in some cases, for going just 1 mph above. To avoid this, it is preferable to travel below the speed limit altogether in the presence of a police unit or out in the open where one may appear suddenly.
Other ways to avoid speeding tickets are as follows:
 Radar detectors
Many motorists use radar detectors to alert them to the presence of a police unit. Contrary to popular belief, radar detectors are not always used to "break the law and get away with it." Some motorists just feel they can relieve their anxiety by knowing in advance when a police unit is around.
Radar detectors are not the ultimate machine for avoiding tickets. Police have other ways of detecting speed, and radar is not always necessary. Some police units use lasers, which cannot be picked up by radar detectors. Other places use aircraft to check speed of vehicles, and these cannot be seen on radar either. Officers also have the ability to follow a vehicle at the same speed to determine its speed.
Tolls exist on some interstates. The tolls could be either for the highways themselves or for bridges along the highways.
Some of the tolls on Interstate Highways for cars are (this list is currently incomplete, not always up to date, and may vary from prices listed by time of day or method used to pay):
New Jersey: As of October 1, 2013, The George Washington Bridge has a toll of $13 while traveling in a northbound direction. The New Jersey Turnpike from exit 7A northward is a part of I-95. The toll for this distance is $9.55.
Delaware: between exit 1 (DE-896) and exit 109 in Maryland (MD-279), there is a $4 toll in each direction. This toll is described by signs as being for the entire Delaware Turnpike, though it only needs to be paid if traveling between these two exits. The toll can be avoided southbound by taking exit 1 north, turning left on Christiana Parkway (DE-4/896), and left on Elkton Road (DE-2/MD-279), then re-entering I-95, or the reverse while traveling northbound. This takes an additional 10 minutes.
Maryland: The Millard Tydings Bridge over the Susquehanna River has a $6 (Will be $8 by July 1st) toll for northbound travelers.
 I-295 (Delaware)
The Delaware Memorial Bridge has a $4 toll for those traveling southbound
 Rest areas
On many interstates are rest areas where motorists can stop to take breaks. Rest areas are usually equipped with rest rooms, and many have various other facilities to meet the needs of travelers.