Here is straight from the USAT website. I know it is long-winded but it is important stuff.

http://rankings.usatriathlon.org/Rules_Officials/rules.htm#Article_V

5.10 Position Fouls.

In accordance with the

Rules as set forth in this Section, a participant is not permitted to

position his bicycle in the proximity of another moving vehicle so as

to benefit from reduced air resistance. While on the cycling course,

participants shall not work together to improve performance,

efficiency, or position by teamwork or other joint conduct. A variable

time penalty shall be imposed for any violation of this section. This

section shall not apply to off-road triathlons and duathlons and shall

be excluded from enforcement at those events.

(a) Illegal Positioning.

Except as otherwise provided in these Rules, while on the cycling

course, no participant shall permit his drafting zone to intersect with

or remain intersected with the drafting zone of another participant or

that of a motor vehicle. With respect to a motor vehicle (including

authorized race vehicles), it is the athlete's responsibility to move

out of the vehicle's drafting zone or to continually communicate to the

vehicle to move away.

(b) Definition of Drafting Zone. The

term "drafting zone" shall refer to a rectangular area seven (7) meters

long and two (2) meters wide surrounding each bicycle. The longer sides

of the zone begin at the leading edge of the front wheel and run

backward parallel to the bicycle; the front wheel divides the short

side of the zone into two equal parts. With respect to a moving motor

vehicle, the "drafting zone" is a rectangular area extending 15 meters

to each side of the vehicle and 30 meters behind the vehicle.

(c) Right-of-Way.

A participant is generally entitled to assume any otherwise proper

location on the cycling course provided that the participant arrives in

the position first without contacting another participant. When taking

a position near another participant, however, a cyclist shall not crowd

the other participant and shall allow reasonable space for the other

participant to make normal movement without making contact.

(d) Blocking. Cyclists who have established the right of way must not block or obstruct the progress of another participant.

(e) Passing.

A participant who approaches another cyclist from the rear or from

another unfavorable position bears primary responsibility for avoiding

a position foul even if the cyclist being approached decreases speed. A

participant must not attempt to pass another cyclist unless adequate

space is available and the athlete is confident of his/her ability to

pass the other cyclist. All passing is to be done to the left of the

cyclist being overtaken unless otherwise specified.

(f) Position.

Except for reasons of safety and when no advantage is gained, all

cyclists shall keep to the right of the prescribed course unless

passing.

(g) Being Overtaken. When the leading

edge of the front wheel of one cyclist passes beyond the front wheel of

another cyclist, the second cyclist has been "overtaken" within the

meaning of these Rules. A cyclist who has been overtaken bears primary

responsibility for avoiding a position foul and must immediately move

to the rear and out of the drafting zone of the passing cyclist. The

overtaken cyclist shall first move completely out of the drafting zone

of the other cyclist before attempting to re-pass the other cyclist. In

no case, however, shall a participant move into the path of another

participant possessing the right of way.

(h) Exceptions. A participant may enter the drafting zone without penalty only under the following conditions:

     (1) When entering the drafting zone from the rear, closing the gap, and overtaking all within no more than 15 seconds.
      (2)
      When cyclist reduce speed for safety reasons, for course blockage, for
      an aid station, for an emergency, when entering or exiting a transition
      area, or when making a turn of 90 degrees or more; or
      (3)
      When USA Triathlon or the Head Referee expressly excludes a section of
      the bicycle course from the position foul Rules because of overly
      narrow lanes, construction, detours, or a similar reason.