"If I have to cancel because of this," he said, "it'll be two months before we can get another appointment."
Openings happen once a day on average on the Tacony-Palmyra, and a little more than five times a week on the Burlington-Bristol, nine nautical miles north.
The Burlington County Bridge Commission uses Nixle, a national text-and-e-mail notification system also used by many police departments and public safety agencies, to alert motorists to imminent openings.
Free of charge, Nixle alerts are easy to sign up for, timely, and reliable - even at 2 a.m.
The Bridge Commission promoted the system vigorously when it launched it 18 months ago, and last week said 4,282 drivers had signed in.
The approaches and toll plazas at the two bridges carry no notice of the alerts, however, and no drivers interviewed during two recent openings at the Tacony knew of them.
Instead, most motorists learn that an opening is underway the way Lyou did - on his way home.
At 5:13, a siren sounded once from the tender's tower near the top of the bridge.
A Bridge Commission police car, its red-and-blue roof lights pulsing, then entered the road from the Route 73 toll plaza in Palmyra. Another entered headed east in the Tacony section of Philadelphia.
Each drove slowly for about 100 yards and then stopped, with the car on the New Jersey side straddling the line between two lanes.
To the south, a large freighter was approaching - about 10 minutes away.
The road's two massive leaves, or steel-grid decks, creaked slowly upright as drivers in two states began hitting the brakes.
Federal law requires lift bridges such as these to open "on demand" for vessels too tall to pass under.
And so, whether it is the pilot of an oceangoing tanker just in from Madagascar, or a frolicking sailboat skipper with a beer in hand, when the bridge tender gets the radio call "Tacony Bridge, Tacony Bridge, this is the vessel," vehicular traffic must give way to maritime.
For these two bridges, with 61-foot clearances above high tide, the calls come day and night, with no pattern.
The three-lane Tacony, which carries an estimated 56,000 vehicles a day, opens a little more than 365 times a year for an average of 12 minutes. For vehicles at the back of the line at rush hour with no way to turn around, however, a delay can run well beyond 30 minutes.
The two-lane Burlington-Bristol, which carries about 24,000 vehicles daily, opens a little more than five times a week for an average of 14 minutes.
"Sometimes it's terrible," said Keith Casella, a welder stuck en route from Cherry Hill to Philadelphia on a recent weekend. "It can take forever to get through."
He said he had been snagged "plenty of times." But this closing, which began at 3:40 p.m., was less frustrating than those that jam him on the way to work.
"This is not so bad," said Casella, who had been sitting for 17 minutes. "I'm going to visit relatives."
Casella, who said he uses the bridge "a lot," said he knew of no notification system that could alert him to bridge openings.
Since May 2012, however, the commission's police department has been sending e-mail or text notices via Nixle.
Typical was this recent notice: "BCBC-PD: The Burlington Bristol Bridge will be opening approx 8:45 a.m. Tacony Palmyra Bridge will then be opening approx 1hr later."
Motorists who wish to receive free Nixle alerts for openings on the two bridges may sign up at www.nixle.com, or click on a link to Nixle at the commission's website at http://www. bcbridges.org/ under "public information."
In addition to imminent openings, Nixle also gives notice about lane closures and accidents.
Drivers who do not want alerts at certain hours, such as at night, may create an account at the Nixle website and specify those hours.
Liz Verna, spokeswoman for the Bridge Commission, said the agency views message signs on the approach to the bridges as impractical.
She noted that there is no alternative crossing near the Burlington-Bristol Bridge, and that for some motorists approaching the Tacony-Palmyra, "it takes more time to change course" to the Betsy Ross than to wait for an opening. Verna said signs at the two bridges advising motorists of Nixle's availability might be a good idea.
The occasional inconvenience may explain why the one-way tolls on the Tacony and Burlington bridges have remained at just $2, said a driver who gave his name as Ben, while a trip to Philadelphia on the Betsy Ross is $5.
Stuck one weekend afternoon on his way from Cherry Hill to visit his girlfriend in Philadelphia, Ben said he gets frustrated when openings happen on the way to work, "but today I really don't mind."
For Lyou, however, the weekday rush hour opening proved a major inconvenience.
"If TP bridge placed a message board with status updates a few miles ahead of the bridge toll station, I would have moved quickly to the alternate bridge," he wrote in an e-mail the next day.
Although "generally happy" with the Tacony, "I was late to my [son's doctor's] appointment (6:15PM)," he wrote. "Thus, I was placed back in patient queue since I was late. Waited about 1 hour in waiting area, actually left the doctor's office at 8:30PM.
Contact David O'Reilly at 856-779-3841 or firstname.lastname@example.org.