In the United States, 14 CFR 91.159 prescribes cruising altitudes for level flight under VFR:
(a) When operating below 18,000 feet MSL and
(1) On a magnetic course of zero degrees through 179 degrees, any odd thousand foot MSL altitude + 500 feet (such as 3,500, 5,500, or 7,500); or
(2) On a magnetic course of 180 degrees through 359 degrees, any even thousand foot MSL altitude + 500 feet (such as 4,500, 6,500, or 8,500).
In other words, planes going generally east use one set of altitudes, and planes going generally west use another set of altitudes.
Now, it's not obvious that these rules are the best possible rules for VFR cruising altitudes. Some alternatives would be:
- No cruising altitude rules at all. All VFR flights select a cruising altitude arbitrarily.
- VFR cruising altitudes are given as blocks instead of single altitudes. For example, planes going generally east cruise at 3,200 through 3,800, or 5,200 through 5,800, and so on.
- Cruising altitudes are prescribed in such a way that aircraft with different courses are always given different cruise altitudes. For example, require aircraft to cruise at an altitude such that the 100-foot needle on the altimeter points in the same direction as the "N" on the heading indicator.
The Wikipedia article "Navigation paradox" mentions a couple of papers which state that random cruising altitudes would result in fewer mid-air collisions than the VFR cruising altitudes prescribed by regulations.
Is there any research suggesting that the current VFR cruise altitude rules do, in fact, improve safety? In other words, are there any studies which compare the current rules to at least one alternative, and show that the current rules are better?
(The specific rules I mentioned are the US FAA regulations, but I'm also interested in research about other countries' VFR cruise altitude rules.)